relation of weather to the yield of corn in Ohio. Let us see what light
his studies shed upon the question at issue between our friends A and B.

Day after day, and year after year, the principal atmospheric
conditions are observed and measured at a great number of points
scattered over the State of Ohio, as they are elsewhere throughout the
Union, and the records thus obtained are carefully compiled, summed up,
averaged and otherwise discussed by officials of the Weather Bureau.
Thus a great fund of detailed statistical information about the weather
is available for comparison with the statistics gathered by other
agencies concerning the yield of crops and their condition at different
stages of growth.

Professor Smith’s analysis of the Ohio records revealed a fact of so
much practical importance that this discovery alone suffices to place
agricultural meteorology among the most fruitful branches of knowledge
cultivated by mankind. He discovered that the success of the Ohio corn
crop depends chiefly upon the amount of rain that falls during the
month of July. The normal rainfall of that month for the State is 4
inches, while the average yield of corn during the past sixty years has
been 34.5 bushels per acre. Comparing the values for individual years,
it is found that the yield is strikingly sensitive to variations from
the normal July rainfall, and especially so when the rainfall is a
little more or less than 3 inches. Near this critical rainfall point, a
variation of _one-fourth inch_ of rain in July means a variation in the
value of the corn crop of Ohio of nearly $3,000,000, and a variation of
one-half inch makes an average variation in the value of the crop of
more than $7,500,000. When the rainfall for July averages over 5 inches
the probable yield of corn will be more than 27,000,000 bushels greater
than it will be if the rainfall averages less than 3 inches. In other
words, this difference of 2 inches in the rainfall for the month of
July adds $13,650,000 to the income derived by Ohio farmers from corn
alone.

Variations of the temperature in July, in Ohio, have been compared with
variations in the yield of corn, with the result that the temperature
of the month appears to have little effect upon the crop. Thus we find
Farmer A to have been right and Farmer B wrong; but both were merely
expressing personal opinions based upon an insignificant sum-total of
experience. Science rests upon a surer foundation.

Although the case of the Ohio corn crop is probably simpler than
most of those that agricultural meteorology has to deal with, for
the reason that a single meteorological element is, in this case, of
decisive importance, it illustrates a rule of quite general application
that has recently come to light; viz., that in the growth of any
particular crop there is usually a rather brief “critical period,”
when it is most sensitive to the influence of weather. For corn, in a
considerable area of the northern United States, this period is July,
or more specifically, in Ohio, the interval from July 11 to August 10.
The rainfall and temperature of other months have, however, definite
though minor influences, which can be evaluated for the same regions.

With respect to the American “corn belt” in general, it is not certain
how far the rules deduced for Ohio are applicable. Professor Smith
has been inclined to look upon July rainfall as the dominating factor
for the whole of that region; so that, for example, a difference of 1
inch in the rainfall (viz., a total for July of 4.4 inches or more,
as compared with 3.4 inches or less) has been held responsible for
an increase of 500,000,000 bushels of corn in the eight principal
corn-growing States. It has also been stated that in the four States
of Indiana, Illinois, Iowa and Missouri an increase of half an inch
of rain in July meant an increase of $150,000,000 in the value of the
crop. These figures have, however, been challenged, and the subject is
still under discussion.

The study of the critical periods of different crops, and the
determination of the amounts of heat and moisture most favorable
to the success of the crop at such periods, may be regarded as the
leading task of the agricultural meteorologist. The most elaborate
researches of this character have been made in Russia by Professor
P. Brounov, who founded in 1896 a meteorological bureau, attached to
the Ministry of Agriculture, with an extensive network of stations
scattered over the Russian Empire. This bureau was quite distinct from
the ordinary meteorological service, under the direction of the Central
Physical Observatory in St. Petersburg. Just before the war Professor
Brounov had 150 stations in operation; most of them for observing the
effects of weather on the leading cereal crops, though some studied
the corresponding relations of horticulture or the animal industries.
Each agricultural station comprised a small plot of land, on which a
certain sequence of crops was grown year after year under conditions
of cultivation as nearly uniform as possible, the only variable factor
being the weather. Meteorological instruments were installed in the
immediate proximity of the plants under investigation. Prior to 1914
Brounov had determined the critical periods of most of the crops grown
in Russia, and had published a great deal of information on this
subject that could be turned to practical account by Russian farmers.

It will perhaps not be immediately apparent to the reader just how
such information can be utilized. Its practical applications vary,
in fact, according to circumstances. First of all, a knowledge of
critical periods and of the weather requirements of crops at these
periods enables the farmer to select his crops and time his farming
operations on the basis of climatic statistics. Brounov published a
series of charts showing the probability of dry weather, as deduced
from many years of observations, for each ten-day period throughout
the agricultural year for every part of European Russia. With such
charts at our disposal, and knowing how long after planting each crop
arrives at its critical period with respect to moisture, we can readily
estimate the probable success of a given crop planted at a given
time and place; at least, so far as this is determined by rainfall.
If temperature or other meteorological conditions are of special
importance at the critical periods, we shall need additional climatic
charts. Of course, the weather in any particular year may differ widely
from the climatic averages; but in the long run crops will prosper in
proportion as their critical periods coincide with the occurrence of
favorable weather as shown by the climatic record. It will be seen
that this is quite a different idea from the traditional one that a
certain crop needs a “moist climate,” another a “hot climate,” etc. The
agriculturist now asks the man of science to tell him _when_, between
planting and harvesting, heat or moisture is of vital importance to the
crop, and _how much_ of each will produce the biggest yield.

In regions where irrigation is practiced it is obviously advantageous
to the farmer to know at what stage of its growth a crop becomes
sensitive to the amount of moisture received. During the greater part
of its life the plant may be quite indifferent to moisture, and at
such times irrigation would be wasteful. The farmer needs to know not
only when the critical period has arrived, but also what the water
requirements are at that period. Too much water may be as bad as too
little.

Even when agricultural practice ignores the rules laid down by the
agricultural meteorologist, a knowledge of these rules may be applied
with great advantage to the prediction of crop yields. It is hardly
necessary to tell any farmer or business man that accurate crop
forecasts are an economic desideratum of the utmost importance. The
United States Government maintains an army of more than 200,000
volunteer crop reporters, supervised by a staff of experts, for
the purpose of determining month by month the condition of every
agricultural crop and its prospective yield. With regard to the monthly
announcements of the Bureau of Crop Estimates, Professor H. L. Moore,
of Columbia University, says:

“The commodity markets are in a state of nervous expectancy as the time
approaches for the official forecasts, because great values are at
stake. It has been estimated that in the case of the cotton crop alone
an error in the forecasts which should lead to a depression of one cent
a pound in the price of cotton-lint would--assuming a crop equal to
that of 1914--entail a loss of eighty million dollars to the farmers.
The vast values at stake and the dangers when no official estimate
is available of the manipulation of the markets in the interest of
speculators are held to justify the large recurrent annual cost of the
employment of the numerous correspondents, clerks, and experts.”

Professor Moore is one of those who have pointed out that the forecasts
based upon the actual condition of the growing crops can be vastly
improved by a mathematical analysis of the weather reports from the
various regions in which the crops are grown. In fact, he goes so far
as to assert that much better forecasts can be made from the weather
reports alone than from reports on the condition of the crops. Whether
or not this view is unduly optimistic, it goes without saying that the
precise data which agricultural meteorology is now acquiring cannot
fail to enhance greatly the accuracy of crop forecasts.

Of course, the weather has always been watched with keen interest by
everybody concerned with the purchase or sale of agricultural products
and has been one of the chief factors determining the rise and fall of
prices. At produce exchanges throughout the United States daily weather
bulletins are received from the agricultural districts, and at many of
them a large weather map is drawn every morning by an employee of the
Weather Bureau detailed for this purpose. The Bureau has made various
other arrangements for supplying the information that is so eagerly
desired concerning the weather as it affects crops, as well as the
animal industries. During the “growing season” in the cotton, corn,
wheat, sugar, rice, broom-corn and cattle-producing areas, designated
centers receive telegraphic reports of rainfall and the daily extremes
of temperature from substations in the regions concerned, and these are
distributed in bulletin form. Each local center, besides publishing
detailed reports from its own area, issues condensed reports from all
the others. The Bureau also issues every week during the agricultural
season a “National Weather and Crop Bulletin,” with text and charts
setting forth the current conditions of moisture, temperature, etc.,
and the state of the crops in all parts of the country.

The use which dealers and farmers make of these weather reports is,
however, very far from having been reduced to science. Some of these
persons, it is true, are frequently able, by a purely instinctive
process of deduction, to make successful forecasts of crop yields from
a close study of the weather, and others have worked out crude rules
of their own for the same purpose; but the agricultural meteorologist
approaches the problem in a different way. Immense progress has
been made in the past decade in applying the mathematical theory of
_correlation_ to this problem. This branch of mathematics, originally
developed chiefly for statistical studies in biology by Galton,
Pearson, and others, is now extensively used by meteorologists not only
for studying the effects of weather on crops, but also for finding
out what correspondences or relationships exist between variations of
weather in different parts of the world, as well as between weather and
sun spots, weather and vital statistics, etc.

Sometimes, when the farmers do not disagree on the subject of
favorable and unfavorable weather for the crops, they hold opinions
in common that agricultural meteorology is unable to substantiate. An
illustration is found in the idea that a good covering of snow during
the winter is favorable to the yield of winter wheat. Apparently this
is one of the host of popular ideas that are based merely on the
delusive foundation of “everybody says so.” Smith has investigated the
statistics of wheat for Ohio and C. J. Root those for Illinois. In both
cases their results negative the prevailing opinion. Professor Smith
finds “some evidence to indicate that wheat has a better prospect if
it is not covered by snow during the month of January,” while Mr. Root
states that, in general, “the winters of light snowfall are followed by
good wheat yields and the winters of heavy snowfall by light yields.”

The study of the relations between weather and crops is really a branch
of a science of broader scope, known as _phenology_. This science is
devoted to the investigation of all periodic phenomena of plant and
animal life that are controlled by the weather. There are, in some
parts of the world, large corps of phenological observers, who maintain
records year after year of the leafing, flowering, and fruiting of both
wild and cultivated plants, the migrations and first songs of birds,
and various other events of a biological character that recur with the
seasons. In the course of time it becomes possible to compute from such
records the normal dates of these events; and then, in any particular
year, a comparison between the actual dates and the normal shows
whether the season is early or late, and by how many days. Phenological
observations on plants also make it possible to draw charts showing the
normal march of the seasons over a country, expressed in terms of plant
life, and such charts are often more valuable to the agriculturist or
horticulturist as a guide in selecting varieties for cultivation and
in timing his operations, than any charts that can be compiled from
ordinary climatic data. Some admirable charts of this kind have been
drawn for parts of Europe.

There are many practical applications of phenology to agriculture,
and there would be more if phenological observations had been made
more extensively throughout the world. Good phenological charts of
different regions would, for example, greatly facilitate the work of
foreign plant introduction carried on by the United States Bureau of
Plant Industry. In the United States phenological observations were
made systematically between 1850 and 1863, but only desultory work has
been done in this line subsequently. The most comprehensive individual
record is that maintained by Thomas Mikesell from 1873 to 1912, at
Wauseon, Ohio, and published in full by the Weather Bureau in 1915.

The old rule of American farmers, inherited from the Indians, that the
time to plant corn is when the leaf of the white oak is “the size of a
mouse’s ear,” illustrates the use that can be made of so-called “index
plants” of the native flora as guides for farming operations. Professor
A. D. Hopkins writes on this subject:

“If such guide plants do not occur on the farm, they can be found among
the ornamental trees and shrubs and hardy flowering plants of other
localities or countries and transplanted. The periodical event of the
falling of the flower catkins of the Carolina poplar has been found to
be one of the best guides to the general early or late character of one
season as compared with the average, while the opening of the leaf buds
and unfolding of the leaves serve as reliable guides to the progress of
spring. The various magnolias in their succession of flowering events
serve as excellent guides to the rate of progress of spring and the
time to do various kinds of work. The ornamental Spiræas, Deutzias,
Diervillas, climbing roses, and Clematis among the ornamentals, and
the dogwood, service tree, redbud, and oaks among the native trees of
the middle and eastern regions of the United States are more or less
constant in their response to prevailing local influences which are
indicative of the time to plant certain field and garden crops. The
opening of the leaf and flower buds and the flowering of the common
fruit trees and shrubs of almost every farm serve as more or less
reliable guides to the time to spray for certain insect and plant
diseases.”

Dr. Hopkins has worked out an interesting rule known as the
“bioclimatic law,” according to which the periodical events of plant
and animal life advance over the United States at the rate of 1
degree of latitude, 5 degrees of longitude, and 400 feet of altitude
every four days--northward, eastward, and upward in spring, and
southward, westward, and downward in autumn. Thus, when the date of
any phenological occurrence is known for one locality, it may be
approximately determined for any other. This law has enabled the
Department of Agriculture to publish rules of general application
concerning the best time to plant winter wheat in order to escape
the ravages of the Hessian fly, thus saving many millions of dollars
to American farmers. The same law is susceptible of various other
profitable uses.

[Illustration: ORCHARD HEATERS IN OPERATION. The economical use of this
method of frost protection depends upon accurate forecasts of the right
time to “fire” the orchard. (_Courtesy of Hamilton Orchard Heater Co._)]

The United States Weather Bureau has been a branch of the Department
of Agriculture since 1890, and a very large share of its routine
work is devoted to the agricultural interests of the country. The
climatological statistics that it has assembled are indispensable in
many departments of agricultural research, besides furnishing varied
information of practical value to farmers. The Bureau has developed a
number of special types of forecasts for the rural industries; such as
predictions, three or four days in advance, of favorable weather for
cutting alfalfa; forecasts of weather unfavorable for sheep-shearing;
notices to fruit growers of dry-weather periods in which fruit trees
should be sprayed; and warnings of the occasional summer showers that
would do so much damage to the great raisin-drying industry of
California but for the vigilance of the forecasters and the efficient
arrangements made by the industry itself for disseminating and acting
upon the warnings. Of course, the ordinary daily weather forecasts,
storm warnings, and cold-wave warnings are valuable in many ways to
agriculturists, and the Bureau has made great efforts to give such
information prompt and general distribution in the rural districts.
The forecasts are generally displayed in post offices, and in many
cases the rural telephone exchanges are pressed into service to
distribute weather information regularly to all their subscribers.
Some exchanges sound a signal every morning when the forecast is ready
for distribution. Lastly, the wireless telegraph and the wireless
telephone, which, in the immediate future, will form part of the
equipment of every up-to-date farm, afford ideal channels for the
dissemination of weather news and are already extensively used for this
purpose.

[Illustration: A SNOW SURVEYOR AT WORK. Note the cylindrical snow
sampler, with its serrated cutting edge, and spring balance for
weighing the sample of snow (_Photographed by J. C. Aller._)]

[Illustration: SNOW ROLLERS, OR WIND-BLOWN SNOWBALLS ON A LAWN AT
POTSDAM, N. Y. (_Photographed by T. J. Moon._)]

There remain to be mentioned the various steps the Weather Bureau
has taken to protect the rural industries from the night frosts of
spring and autumn, in the shape of special forecasting arrangements,
the publication of frost charts, and a wide range of scientific
investigations. The Bureau’s undertakings in this line are merely a
part, though a leading one, of a great campaign of frost protection
that is being carried on by scientific and official agencies in this
country on a larger scale than anywhere else in the world.

Frosts, classified according to their severity as “light,” “heavy,”
and “killing,” are most likely to occur in spring and autumn, when
an extensive area of high barometric pressure brings its usual
accompaniment of clear skies and calm nights. They are predicted on
a general scale from the weather map, and locally from indications
of temperature and humidity and a knowledge of important topographic
influences, such as those due to hills and valleys and neighboring
bodies of water.

In agricultural usage the term “frost” is applied to the occurrence of
a temperature low enough to kill or injure tender vegetation, such as
growing vegetables or the buds, blossoms, and fruit of fruit trees. The
occurrence of a frost, in this sense, is not necessarily identical with
the deposit of ice crystals known as “hoarfrost.” Different species
and varieties of plants are, of course, susceptible in very different
degrees to the effects of low temperature; i. e., they differ greatly
in “hardiness.” In the case of fruits and vegetables the danger point
generally lies a little below the freezing point of water (32 degrees
F.).

The occurrence of frost is favored by the rapid cooling, by radiation,
of the earth and its plant covering, which goes on at night under a
clear sky and in still air. Under these conditions a layer of stagnant,
cold air forms close to the ground, with warmer air lying above it. The
difference in temperature at different levels is often so pronounced
that fruit on the lower branches of a tree is killed while that growing
on the higher branches remains uninjured. Similarly, frost will occur
in the bottom of an inclosed valley but not on the surrounding slopes.
In the case of a valley the layer of cold air that forms at the bottom
is commonly deepened by additional cold air draining down from the
hills.

Many large orchards have their “warm spots” and their “cold islands” or
“north poles,” well known to the orchardist; due in some cases to the
nature of the soil rather than to topography. Certain mountain regions
in North Carolina are famous for their “thermal belts” or “verdant
zones”; i. e., areas part way up the slopes that escape the frosts
occurring both above and below them. These frostless belts, which have
been the subject of numerous investigations for three-quarters of a
century, seem to mark the upper level of the pool of cold air that
collects in the valley by drainage from the mountainsides. A detailed
temperature survey of the thermal belt region of North Carolina was
made during the years 1912-1916 by the United States Weather Bureau
and the North Carolina State Board of Agriculture. In some places the
minimum temperature at night was found to be 15 or 20 degrees higher in
the thermal belt than at the bottom of the valley, a few hundred feet
below.

Clouds, by checking radiation from the earth, and wind, by mixing
the colder and warmer layers of air together, both prevent frosts
that would otherwise occur. Artificial methods of protection include
covering plants with screens of wood, paper, or cloth, building smudge
fires to provide a blanket of smoke (a method of doubtful value),
and, above all, heating by means of wood fires or various types of
“orchard heater,” burning either oil or coal. An elaborate technique
of orchard heating has been developed, having in view especially the
most economical use of fuel and labor consistent with the object to be
attained. In many cases orchards are provided with alarm thermometers,
which ring a bell when the temperature approaches the danger point in
the orchard.

The local prediction of frost from the readings of meteorological
instruments is a problem that has not been fully solved. The idea
formerly prevailed that the temperature of the dew point, as determined
from readings of the dry-bulb and wet-bulb thermometers in the early
evening, was a safe guide to the fall of temperature to be expected
during the night, but this belief has not stood the test of accurate
observations. At the present writing certain formulas involving data
of both temperature and humidity are being used experimentally by
Weather Bureau specialists for predicting the lowest temperature of
the night when the general conditions indicate that frost is possible.
A comprehensive discussion of this subject has been published by
the Bureau as Supplement No. 16 of the “Monthly Weather Review.”
(Washington, 1920.)

CHAPTER XVI

COMMERCIAL METEOROLOGY

It is a significant fact that the American Meteorological Society,
which was organized in 1919, has a Committee on Commercial Meteorology.
The appointment of this committee was one of the earliest tokens of
the fact that the applications of meteorology to business, always
recognized to be important and far-reaching, had at last been
segregated as a distinct field of inquiry. The time is near at hand
when this field will have its corps of specialists and its textbooks.
Courses in commercial meteorology will be given in business colleges,
and meteorologists will be attached to the staffs of large business
enterprises. The chamber of commerce of a wide-awake western city
already maintains a Department of Meteorology, with a former Weather
Bureau official at its head, and “consulting meteorologists,” now
practicing their novel profession in other parts of the country, find
their principal clientele among business concerns.

Weather not only influences most kinds of business, but is the
foundation of many of them. Plenty of illustrations of the latter fact
will be found in every large department store. Umbrellas, rubbers,
and mackintoshes are made and sold because of rain; their best market
is in countries with rainy climates, and their sale from day to day
fluctuates with the state of the sky. Electric and palm-leaf fans
are a drug on the market or the reverse, according to the readings
of the thermometer. Sleds and ice skates are sold where and when the
weather is cold. This list may be prolonged _ad lib_. If we leave the
department store and walk along any business thoroughfare, we shall
discover other striking examples of commercial undertakings that owe
their existence chiefly or entirely to the weather. Abolish cold
weather and you abolish the dealer in furnaces and heating stoves,
besides reducing the rank of the coal-dealer considerably below the
“baronial” level. Eliminate hot weather from the meteorological program
and the ice dealer will likewise tumble from his high estate.

All this is so obvious that it seems hardly worth while setting down;
and yet the paradox must somehow be explained that business men
have not, in general, paid much attention to meteorology, and that
they have made only fragmentary use of the official meteorological
establishments that were created, in part, for their benefit. Probably
this paradoxical situation is merely a case of mental inertia. During
the long ages of traffic before there were any weather maps, scientific
weather forecasts, or climatic statistics, the weather was necessarily
an unknown quantity in the mathematics of buying and selling. That it
is not so to-day is a fact to which the business mind has been very
slow in adjusting itself.

We have mentioned some of the obvious relations of weather to commerce,
but there are others that are not so obvious. Many of these are
indirect. Thus the effects of the weather on agriculture are nearly
always reflected in the commercial world. It is not the farmer alone
who suffers from a prolonged drought, for example. It has been
asserted that every severe financial panic in our history has been
closely associated with a protracted period of deficient rainfall, and
that there has been no period of protracted drought without a severe
financial panic except one that occurred during the Civil War. Mr.
H. H. Clayton, who published this assertion in 1901, has cited the
case of the wheat crop as illustrating the magnitude of the effect
that rainfall exercises on economic conditions in general through its
effects on agriculture.

“If,” he says, “the amount of wheat raised in the United States were
reduced one-half or even one-third by a year of deficient rainfall, it
is easy to imagine an enormous strain on the business of the country,
and with a succession of such years the effect might mean disaster.
Such a deficiency in the wheat supply, with wheat at 80 cents a bushel,
would mean for a single year a direct loss in wealth of more than
$100,000,000; it would mean that nearly all the wheat which is usually
shipped abroad would be needed at home; it would mean that thousands of
railroad cars and ships which ordinarily transport this grain would lie
idle, that thousands of men who usually handle this grain in transport
would be out of employment, that farmers in large numbers would be
unable to meet their obligations, and consequently that banks and
business of all kinds would suffer.” Recent prices of wheat give added
force to these statements.

In contrast to such broad relations of the weather to business, it may
be interesting to point out certain relations which are of so special
a character that, although familiar to hosts of business men, they
have generally escaped the attention of writers on economics. On this
subject Mr. John Allen Murphy says:

“Retail sales are influenced tremendously by the weather. This is one
factor that makes it impossible for a retailer to equalize the peaks
and valleys in his sales chart. Favorable weather will bring him a
rush of business. A bad day will keep patrons from his store. There is
nothing he can do to prevent it. Many merchants have tried the plan of
offering ‘stormy day specials,’ but at best such a scheme is only a
makeshift that seldom works. The weather also affects the buying moods
of people. A dark, dreary day in summer seems to influence humans to
take on the same cast as the atmosphere. They are grouchy and hard
to please. On the other hand, a cold day in winter has the opposite
effect. The warmth and cheer of the store is such a pleasant contrast
to the out-of-doors that shoppers like to linger over the wares and
indulge themselves more readily in the luxury of buying.

“A stormy day or a series of them always helps the mail-order business.
In such weather people are inclined to stay at home. In passing the
time, they are likely to thumb the pages of such catalogues as they
have and thus see in them articles that they want. On the farm,
especially in the bleak days of winter, it is often the custom to order
garden seeds, incubators, tools, and many other things that will be
needed as soon as spring opens up. On a bad day traveling salesmen find
it easier to get the ear of a merchant. Not being busy with customers,
he is prone to be more lenient toward the ‘boys with the grips.’”

Another writer on this subject, Mr. F. C. Kelly, says:

“In a large city, the business of a department store is seriously hurt
by rain in the forenoon, but rain in the early afternoon is usually
a big help. Most customers of a big-city department store are women,
and nearly all of them live some distance from the store--at the edge
of the city or in the suburbs. If it rains along about eight or nine
o’clock in the morning, the woman who had planned to go shopping
that day is quite likely to change her mind, even though she did not
intend to go until afternoon. The rain not only suggests discomfort in
getting about, but diminishes her desire or immediate need for certain
articles, and drives the shopping idea out of her head. On the other
hand, if it is bright and clear in the morning, but clouds up about
noon for a heavy downpour which lasts most of the afternoon, it is
the best thing that could happen for the department store, because
shoppers get in and cannot comfortably get out. They shop all over the
store, buy luncheon there, and shop some more. While the rain is thus
helping the department stores, it may hurt the smaller shops, because
many customers who would otherwise look around are obliged to do their
buying all under one roof.”

No aspect of business more faithfully reflects the weather, or, in
a somewhat less degree, the weather forecasts, than advertising. So
important is it, in many lines of business, to make advertising fit
the weather that one might expect merchants to be, as a class, as
weather-wise as sailors and farmers. A page of advertising in a great
metropolitan newspaper is a costly investment. If, for example, it
invites the public to pay a Sunday visit of inspection to some haven
for homeseekers in the suburbs and Sunday turns out to be the kind
of day that converts building-lots into bogs, the advertiser will
perhaps be led to inquire whether there is not some means of avoiding
another such fiasco; and he may thus make the surprising discovery that
meteorology is not entirely a theoretical science. The conjunction of a
conspicuously advertised sale of rubbers and a soppy week-day morning
may be either a lucky accident or the result of studying the weather
map. In the former case, supposing the business to be conducted in
the northeastern United States, where dry weather is about twice as
common as wet, the odds would be two to one against the occurrence even
of light showers on the day the advertisement appeared, and three or
four to one against the occurrence of such weather as would make the
advertisement decidedly _à propos_.

These remarks about newspaper advertising are, to a great extent,
applicable also to the dressing of windows and the display of goods
inside the shop. In both cases a moderate amount of foresight in the
matter of weather will result in placing before the customer the right
goods at the right time. One of the minor ways in which the merchant
can turn the science of meteorology to advantage consists of using
meteorological instruments and the official weather forecasts and
bulletins for the purpose of attracting attention to his windows or
to his stock-in-trade. The drug-store thermometer is the illustration
of this process that comes first to one’s mind. There is no reason
why, with the progress of civilization, this celebrated instrument
should not be made a trustworthy index of temperature as well as an
effective advertisement. In continental Europe weather instruments are
displayed along with miscellaneous advertising matter in many of the
street “weather columns” (_Wettersäulen_), which furnished the idea of
the meteorological kiosks installed by the Weather Bureau in American
cities.

One of the most important branches of commercial meteorology relates
to the effects of weather upon transportation. This is a many-sided
subject. In the first place, the railway and steamship companies,
and other concerns engaged in the transport of goods and passengers
have their manifold weather problems, among which one may mention,
at random, that of dealing with the snow blockades of railways,
precautions against the skidding of taxicabs in wet weather, the
avoidance of iceberg-infested routes at sea, and the selection of
climatically favorable sites for aerodromes. The shipper has a somewhat
different, but overlapping set of weather problems.

“In the building of railroads,” says Mr. E. L. Wells, “many phases of
climate are to be considered, including the probability of floods,
deep snows, high winds, sand storms, etc. It is not long since a
considerable length of railroad line in one of the Western States
was found to be practically worthless because of having been built
too near the bed of a stream and therefore being too much subject to
damage from floods, so it was replaced by a line built higher up. The
writer remembers two railroads entering the same town in one of the
northern plains States, one of which is seldom blockaded, while the
other is sometimes closed by snow for months at a time. In the former
case the cuts are parallel to the wind, while in the latter the wind
blows directly across the cuts. In operating railroads a knowledge of
the climate is essential. This is particularly true in the shipment
of perishable products, which may require icing or ventilation as a
protection against high temperature, or insulation against cold.
Not only is a knowledge of climatic conditions essential in taking
precaution against loss in transportation, but weather records are
playing an increasingly large part in the settlement of claims for
products and property damaged in transit. The claim agents of the
leading transportation companies and the traffic managers of the
commission houses and producers’ associations keep complete files of
climatological data, and a large percentage of claims for damaged
goods, whether they be for a trainload of chilled bananas or for a
traveling man’s samples ruined by rain, are now settled out of court on
the basis of the weather records. Claims for car demurrage are often
settled on the basis of the weather reports.”

Detailed information concerning the effects of temperature on all sorts
of food products, both in transportation and in storage, was collected
by the Weather Bureau some years ago and published as the Bureau’s
Bulletin No. 13.

While the domestic shipper can easily obtain from the Weather Bureau
detailed climatic statistics for all parts of the United States, as
well as the current weather reports for this country, and can profit
greatly by regulating his operations in accordance therewith, it
is not quite so easy for the shipper to foreign markets to obtain
the corresponding data of foreign countries. With the expansion
of our foreign trade, the demand for such data has grown to large
proportions. The Weather Bureau, which has an unrivaled meteorological
and climatological library in Washington, is naturally the place
where such data are most frequently sought, but the labor entailed in
extracting and digesting the information in response to individual
requests is often too great to be undertaken by a Government office,
where the time of the employees is absorbed in routine duties. There
is, therefore, a promising field here for the private commercial
meteorologist. Unofficial work in this line is already carried on to
some extent. Thus a great steel company in New York has a salaried
“consulting geographer” on its staff, who advises on meteorological
questions. One of the problems he has been called upon to solve was to
determine the proper dates for shipping steel from Atlantic and Pacific
ports of the United States to various places in India, so that it would
never arrive during the monsoon rains. Records of current and very
recent weather in distant countries are, in a great majority of cases,
unobtainable anywhere in the United States. The interchange of detailed
weather reports between the different meteorological services of the
world involves in the first place, with few exceptions, a painfully
slow process of publication, and then distribution by mail; so that,
for example, records of observations at some places in South Africa
or Australia, or even many parts of Europe, do not reach the Weather
Bureau Library, in Washington, until two or three years after the
observations are made. Undoubtedly the time will come--and probably in
the near future--when there will be a world-wide exchange of weather
news by wireless telegraphy.

One kind of business wholly dependent upon the weather, which we have
not yet mentioned, is weather insurance. There are several kinds, but
hail insurance and tornado insurance are those extensively practiced;
the former much more widely and systematically in the Old World than
in the New, while the latter is confined to America. Insurance
against frost is said to have been practiced in Germany, and there
appears to be an excellent field for it in the United States. The
insurance of outdoor events, such as games, shows, and _al fresco_
parties, against rain has been carried on for a good many years by
speculative underwriters at Lloyd’s, in England, and has more recently
been undertaken in this country. Of course the weather element enters
to a considerable degree into other kinds of insurance. Ordinary
marine insurance is, to a large extent, insurance against storms; fire
insurance is partly insurance against lightning; window and plate glass
insurance involves the risk of breakage by wind and hail; and even life
insurance is greatly concerned with the effects of weather and climate.

CHAPTER XVII

MARINE METEOROLOGY

That it behooves a sailor to be weather-wise has always been admitted,
but there was a time, almost within the memory of men now living, when
neither seamen nor landsmen had the remotest conception of the benefits
that a systematic study of the meteorology of the sea was capable of
conferring upon the maritime world. The man who first grasped the
importance of such a study and translated his ideas into facts was the
American naval officer, Lieutenant Matthew Fontaine Maury.

During his brief career at sea Maury became impressed with the
meagerness of the information then available concerning the winds and
currents that aid or hinder the voyages of sailing ships. When, in
consequence of an accident that incapacitated him for shipboard duties,
he was assigned to service in Washington, he began to explore the old
logs of naval vessels, filed in the Navy Department, for notes on
meteorological conditions, and eventually developed a plan of securing
regular observations from both the Navy and the merchant marine. The
result of this undertaking was the publication of the famous Wind and
Current Charts, which revolutionized navigation throughout the world.

The practical value of these charts, of which 200,000 copies were
distributed to the masters of merchant vessels of all nationalities,
was promptly recognized. By taking advantage of the favorable winds
and currents shown on the charts, and avoiding those that were
unfavorable, mariners were able to reduce the average time of a sailing
voyage between the Atlantic and Pacific ports of the United States
by forty days. The money value of the charts to vessels sailing from
the United States to South America and the Far East was estimated at
$2,250,000 per annum. British shipping on all seas is said to have
benefited to the extent of $10,000,000 per annum. Neither was the
utility of the charts limited to the saving of money. The following
episode is cited in Maury’s biography:

“When the _San Francisco_, with hundreds of United States troops on
board, foundered in an Atlantic hurricane, and the rumor reached port
that she was in need of help, everyone looked to Maury as the only man
in the country who could tell where to find the drifting wreck. To him
the Secretary of the Navy sent for information. He at once set to work
and showed how the wind and currents acting upon a helpless wreck would
combine to drift her ‘just here’, pointing to a spot on the chart,
and making a cross mark with the blue pencil he had in his hand. Just
there the relief was sent, and just there the survivors of the wreck
were picked up. This was an incidental result of his study of winds and
currents.”

A further outcome of Maury’s enterprise was the holding, at his
suggestion, and by invitation of the United States Government, of an
International Maritime Conference, which met in Brussels in 1853,
and worked out a world-wide plan for meteorological observations at
sea. The work thus begun has since been carried on by the leading
maritime nations of the world. In the United States the duty of
gathering weather reports on a uniform plan from vessel masters has
been intrusted, at different times, to the Hydrographic Office, the
Signal Service, and the Weather Bureau. It is now performed by the
last-named institution, through its Marine Division, but the Pilot
Charts and books of sailing directions (“Pilots”) in which the compiled
information is published, are issued by the Hydrographic Office of the
Navy.

The modern successors of Maury’s Wind and Current Charts are,
especially, the Pilot Charts for the different oceans issued monthly
in Washington, and the monthly charts of similar character published
by the British and German governments. Apart from these periodical
publications, valuable collections of meteorological charts for oceans
or smaller marine areas have been published by the British, German,
Dutch, Indian, Japanese and other authorities.

The value of such publications has not been lessened by the gradual
substitution of steam for sails on ocean-going vessels. While wind is
no longer all-important, it is a factor in determining the speed, and
hence the earning capacity, of all classes of ocean shipping, and the
same is true of marine currents. Fog and drifting ice are, in general,
more serious obstacles to steamers than to sailing ships. A glance
at one of the Hydrographic Office Pilot Charts will suffice to show
that these publications are indispensable to the mariner. On these
charts we find, first of all, in the center of each five-degree square
of latitude and longitude a “wind rose” showing the frequency of the
winds that have been observed in that region from each of the cardinal
points, and their average force from each direction. On the charts
will also be found the routes recommended for full-power and low-power
steamers and sailing vessels, lines of magnetic variation, tracks of
storms in past years for the month in question, location and force of
currents, average limits and prevalence of fog for the month, recent
information about drifting ice and derelicts, descriptions of storm
signals, and an abundance of other information of vital importance to
the seaman.

[Illustration: OCEAN WEATHER MAP PREPARED FROM VESSEL REPORTS

JAN. 11, 1913, GREENWICH MEAN NOON

_U. S. Weather Bureau_

Solid black lines are isobars. Arrows fly with the wind, the center of
the arrowhead marking the position of the vessel, and the number of
feathers denoting the force of the wind on the Beaufort scale. Shading
of the head shows degree of cloudiness.]

Most of the material used in the preparation of the charts above
described is obtained from a great corps of volunteer marine observers,
who enter their observations at stated hours in forms provided for
the purpose and send these records to the establishment in charge
of the work at the end of each voyage. The forms furnished by the
United States Weather Bureau prescribe only one regular observation
a day, to be taken at Greenwich mean noon. Each observation shows
the position of the ship, the direction of the wind, the force of
the wind on the Beaufort scale, the height of the barometer, the
readings of the dry-bulb and wet-bulb thermometers, the temperature
of the water at the surface, the state of the weather, and the kind,
amount, and movement of clouds. In order to check the accuracy of the
barometric readings, the observer is instructed to read his barometer
at prescribed hours on three successive days when in port and send the
readings to the Weather Bureau. On receipt of these readings the Bureau
compares them with those of the nearest meteorological station, and
then mails the observer a “barometer tag,” showing the results of the
comparison and the error of his instrument. Besides keeping up these
routine observations, the observer keeps a record of fog encountered
at any hour of the day and makes detailed reports on storms. Many
marine observers also report observations at stated hours by wireless
telegraphy.

The enormous fund of information thus collected over the ocean is
applied to several purposes besides the construction of Pilot Charts.
Our Weather Bureau and certain foreign meteorological institutions
prepare daily charts, showing approximately the instantaneous
conditions over great oceanic areas, especially the North Atlantic.
These maps are analogous to the daily weather maps published for land
areas, but the drawing of each map is, necessarily, delayed for
several months after the date to which it refers, in order to allow
time for the receipt of as many reports as possible from ships at sea.
As a rule such charts are prepared in manuscript only, but, though they
cannot be distributed after the manner of ordinary weather maps, they
are valuable for studies in the institution itself on the movements
of storms and other atmospheric processes. They also enable the
meteorological officials to answer inquiries concerning the winds and
weather that have prevailed over a particular part of the ocean on any
specified date. Such inquiries come from vessel owners, underwriters,
and others, and the replies are frequently used as evidence in
admiralty suits.

In the case of one series of such maps--viz., the daily synoptic
charts of the North Atlantic, begun by Niels Hoffmeyer, of Copenhagen,
and now prepared jointly by the Danish Meteorological Institute and
the Deutsche Seewarte, in Hamburg--the charts have actually been
published and sold, though they are so costly that the number of sets
in libraries throughout the world is probably small. These remarkable
charts present daily pictures of the winds and barometric pressure over
the North Atlantic Ocean and the adjacent continents from 1873 to 1876,
and from 1880 down to a recent date.

From what we have already said it will be seen that the marine
observers cooperating with the United States Weather Bureau and kindred
institutions abroad are all contributing toward the great task of
recording the history of the weather over the oceans from day to day
and assembling data that can be digested in the form of marine climatic
statistics and used as the basis for many scientific investigations.
This concerted undertaking does not, however, constitute the whole
scope of marine meteorology. Every intelligent mariner finds it
necessary to acquaint himself with the laws of the winds, indications
of coming storms, means of determining the proximity of icebergs, the
systems of storm signals used in different countries, the method of
constructing weather maps from wireless bulletins, etc. He ought, in
short, to become an accomplished meteorologist.

One of the classic problems of the navigator is that of handling his
ship in a violent cyclonic storm, especially a tropical hurricane. The
reader will recall that a cyclone, besides traveling as a whole at a
rate of several hundred miles a day, consists of a system of winds
rotating around the center. The result of this double motion is that
the winds on one side of the center are not only more violent than
those on the other, but they are also so directed as to drive a vessel
running before the wind, across the storm track ahead of the advancing
center, while those on the other side tend to drive a vessel to the
rear of the storm. The two halves of the storm area are accordingly
known as the “dangerous” and “navigable” semicircles, respectively.
While this simple statement sets forth the fundamental facts involved,
the actual problem is complicated by many features, such as the fact
that the winds do not blow in circles, but more or less spirally, that
the area of the storm cannot be readily determined, that two storms may
occur in close proximity to each other, etc.

The accompanying diagram, published by the United States Hydrographic
Office, represents a cyclonic storm in the northern hemisphere, the
circles being isobars, or lines passing through places at which the
same barometric pressure prevails (indicated in inches), and the arrows
indicating the direction of the winds. The diagram is thus explained:

“For simplicity the area of low barometer is made perfectly circular
and the center is assumed to be ten points to the right of the
direction of the wind at all points within the disturbed area. Let
us assume that the center is advancing about north-northeast, in the
direction of the long arrow, shown in the heavy full line. The ship _a_
has the wind at east-northeast; she is to the left of the storm track,
or technically in the navigable semicircle. The ship _b_ has the wind
at east-southeast and is in the dangerous semicircle.***A vessel hove
to at the position marked _b_, and being passed by the storm center,
will occupy successive positions in regard to the center from _b_ to
_b_4, and will experience shifts of the wind, as shown by the arrows,
from east through south to southwest. On the other hand, if the storm
center be stationary or moving slowly and a vessel be overtaking it
along the line from _b_4 to _b_, the wind will back from southwest to
east, and is likely to convey an entirely wrong impression as to the
location and movement of the center. Hence it is recommended that a
vessel suspecting the approach of proximity of a cyclonic storm should
stop for a while until the path of the center is located by observing
the shifts of the wind and the behavior of the barometer.”

The movement of the winds around the storm center shown in this diagram
is that of cyclones of the northern hemisphere; i. e., contrary to the
direction of the clock hands. In the southern hemisphere they blow in
the opposite direction around the center.

[Illustration: NAVIGATION OF A SHIP IN A CYCLONIC STORM

(_U. S. Hydrographic Office._)]

By observing the rise or fall of the barometer, the shift of the
winds, and the state of the sea and sky, the experienced navigator
is generally able to lay down on a chart the approximate position of
the storm center and steer his vessel so as to avoid danger. Various
devices, known as “storm cards,” “cyclonoscopes,” etc., have been used
to aid in the process of locating a storm from shipboard observations.
In the Far East mariners use for locating typhoons an ingenious
combination of the storm card and the aneroid barometer, called the
“barocyclonometer,” an invention of the Rev. J. Algué, director of the
Philippine Weather Bureau.

The most important development in marine meteorology in recent years
has been the rapidly increasing use of radiotelegraphy, both by marine
observers in transmitting reports of observations to shore and to other
ships, and by meteorological institutions in issuing weather bulletins
and storm warnings to vessels at sea. The first regular undertaking
in this line was carried out under the auspices of the London _Daily
Telegraph_ in the year 1904. This newspaper arranged with some of
the leading transatlantic steamship lines to furnish weather reports
by wireless from their vessels, and these reports were published in
its columns for several months. The following year the United States
Weather Bureau began, in a tentative way, the collection of wireless
weather reports from off-shore vessels, and similar undertakings were
soon afterward launched in other parts of the world, but for some years
such reports were of little practical value, owing to the limited range
of wireless communication.

[Illustration: A SHIPBOARD WEATHER MAP

Vessels off the American coast can make their own weather maps every
night, using data supplied at fixed hours by high-power radio stations
(shown by stars on the map), together with radio reports from other
vessels. Letters near stations are the code letters used in wireless
bulletins to describe the stations. Vessel reports are indicated by
names. Arrows show direction of wind and the force on the Beaufort
scale (shown by the number of feathers). Besides data for constructing
maps, the radio stations issue forecasts and storm reports for each of
the numbered zones shown off the Atlantic coast and over the Gulf.]

At the present time wireless reports from ships on the Atlantic enable
the forecasters on both sides of that ocean to extend the areas of
the weather maps on which their predictions are based, and reports
from ships are also received to a limited extent by forecasters on our
Pacific coast as well as in the Far East, India, and elsewhere. In
this country such reports have been especially valuable in indicating
the movements of West India hurricanes, and thus have helped to solve
the problem of protecting the vast tonnage that has been attracted
to Caribbean waters by the opening of the Panama Canal. The reciprocal
process of transmitting weather intelligence to vessels by wireless
bulletins, broadcasted at certain hours every day by high-powered
radio stations, has made much more progress. Such bulletins include
information concerning the current and prospective weather, winds and
storms over specified ocean areas, as well as reports of observations
made at a number of land stations, from which it is possible for
vessels at sea to construct their own weather maps. They are thus
enabled to take advantage of favorable winds and to avoid unfavorable
winds and storms. Wireless weather reports from other vessels help to
piece out these shipboard maps.

The meteorological services of all civilized countries adjacent to
the sea display signals along their coasts to announce the coming of
storms dangerous to navigation. One of the earliest devices used for
this purpose was the “aeroclinoscope,” a form of semaphore formerly
employed by the meteorological service of Holland. The position of the
arm of the semaphore indicated the region in which the barometer was
low; i. e., the storm center. In the British Isles, in the middle of
the last century, Admiral FitzRoy introduced the use of canvas cones
and “drums” (i. e., cylinders), which, seen from any direction, have
the appearance of solid triangles and squares against the background of
the sky. The British later abandoned the drum and used the cone only,
pointing up or down for northerly or southerly gales, respectively.
The American storm flag--red with a square, black center--was adopted
by the United States Signal Service (the predecessor of the Weather
Bureau) in 1871. This signal was subsequently amplified by the addition
of red and white pennants to show the expected direction of the wind
at the beginning of the approaching storm. Most countries use lanterns
for night storm signals. In the year 1909 a uniform system of signals,
consisting of cones by day and lanterns by night, was recommended for
use in all countries by an international commission which met in London.

In spite of this recommendation some thirty or forty different systems
of daytime storm signals are now in use in different parts of the
world. On the China coast an elaborate system of signals, consisting of
cones, balls, diamonds, and squares displayed on a mast and yardarms,
indicates the existence of a typhoon anywhere in the neighboring seas,
together with its location and movement.

CHAPTER XVIII

AERONAUTICAL METEOROLOGY

During the great war the British Government decided, in its wisdom,
to establish a flying field in Scotland, at which aviators were to be
trained in dropping bombs. The commission having this matter in hand
chose a site on the shores of Loch Doon. In laying out the field a
bog had to be drained; then a railway was constructed, hangars were
erected, and other operations were carried out, entailing altogether an
expenditure of half a million pounds. At a certain late stage in the
proceedings the disconcerting discovery was made that the field could
never be successfully used for the purpose intended, on account of the
gusts and eddies produced by the surrounding hills. The undertaking
was therefore abandoned. The authorities had presumably enlisted the
skill of engineers from the outset of the work--but they had failed to
consult a meteorologist!

A few such object lessons seem to be necessary to demonstrate the
fact--which ought to be obvious--that meteorology is an indispensable
and vital adjunct of aeronautics. This fact is now pretty well
understood. Nearly all the activities of mankind are more or
less influenced by weather, but few, if any, to such an extent
as aeronautical enterprises. Hence a definite branch of applied
science--Aeronautical Meteorology--is rapidly taking shape. Already it
enters into the curriculum of aeronauts; it has profoundly modified the
methods of the ordinary meteorological services of the world; and it
is raising a crop of specialists, some of whom are now employed by the
business firms that manufacture or operate aircraft.

The statement has constantly been made since the war that aeronauts
are becoming “independent” of the weather. This statement has a grain
of truth in it, but no more. It is a fact that, under war conditions,
aviators flew in every sort of weather, and often with impunity. Even
since the war commercial aircraft have negotiated adverse atmospheric
conditions with remarkable success. A spectacular feat of this sort was
achieved on August 28, 1919, when a passenger-carrying aeroplane on the
Paris-London route, piloted by Lieutenant Shaw, flew over this route
through a hurricane blowing in gusts of from 40 to over 100 miles an
hour, accompanied by a torrential rainstorm and such poor visibility
that the pilot was frequently obliged to fly very low in order to pick
up his landmarks and make sure that he was on his course. The flight
was accomplished in 1 hour and 50 minutes--about half an hour less than
schedule time. It is said that “the two passengers in the cabin of the
machine emerged without any appearance at all of strain”--such as they
certainly would have experienced if they had made the crossing by the
Channel steamer on that boisterous day. In fact the land and sea route
was seriously disorganized by the storm, and the Continental trains
were arriving in London hours late.

Lest hasty conclusions should be drawn from this episode it should be
stated at once that the company operating the air route in question,
far from considering itself independent of weather, is not content
with the detailed bulletins furnished to aeronauts by the British
Meteorological Office (which specializes in aeronautical meteorology
more extensively than any other official weather service in the world),
but maintains an elaborate weather service of its own, with an able
meteorologist at the head of it.

An accurate statement of the situation would be that wind and weather
are no longer the grave dangers that they once were to the aeronaut;
but they are still, and will probably always be, factors of the utmost
importance in the successful and profitable operation of aircraft. In
order to make this matter plain it will be necessary for us, first
of all, to devote a few words to some of the fundamental principles
involved in aerial navigation.

The layman who sees nothing mysterious in the ascent of a balloon is,
in general, somewhat puzzled by the phenomenon of a heavier-than-air
machine rising from the ground. Yet, in both cases, the ascent of the
vehicle depends upon the fact that air is not just empty space, but a
material substance, possessing density, weight, and other properties
many of which pertain also to solids. A balloon rises not because
it is light, but because the air about it is heavy. In other words,
gravity pushes the air under the balloon more forcibly than it pulls
the balloon downward. The ability of an aeroplane to leave the ground
depends upon the fact that air offers resistance to bodies moving
through it.

        A                                B
        |                                   /
        |                                  /
        |                                 /
  ------|------->                 -------/------>
        |                               /
        |                              /
        |                             /

THE EFFECT OF AIR RESISTANCE ON AN AEROPLANE]

Suppose a vertical plane (A)--such, for example, as the wind shield
of an automobile--is moving horizontally through still air. The
resistance of the air impedes its motion, and a part of the motive
power is employed in overcoming this resistance. Now, suppose the
plane (B) is nearly, but not quite, horizontal, and is propelled by a
force tending to make it move in the direction indicated by the arrow.
This is approximately the case of an aeroplane driven by a motor; the
plane representing the wings of the machine. Only a part of the air’s
resistance is now effective in impeding the forward motion of the
plane. The rest of it pushes the plane upward. If you hold your hand
at such an angle and move it through water you will feel an analogous
upward push. Moreover, you will notice that the faster you move your
hand the greater is the push. Not only does this upward pressure of
a fluid upon an inclined plane moving through it vary with the speed
of the latter (to be exact, as the square of the speed), but it also
varies with the angle which the plane presents to the fluid in its
path. If the wing of an aeroplane, for example, cuts the air nearly
edgewise, the upward pressure will be slight. As it departs from an
edgewise position, (with the front edge higher than the rear), the
upward pressure increases, but not indefinitely; beyond a certain
rather small angle it begins to diminish.

In an aeroplane the upward pressure, or “lift,” is increased by giving
the wings a slightly arched shape, or “camber.” The air flows over the
arched wings in such a way as to produce a suction above them which
helps the push from below. The actual amount of lift for a given speed
has been determined by experiments for wings of various shapes and
sizes and set at various angles to the line of motion. If, when the
machine is in the air, the lift is just sufficient to counterbalance
the weight of the aeroplane, the latter flies horizontally. An increase
in lift causes the machine to rise; a decrease in lift permits gravity
to pull it down.

Now suppose the aviator is flying horizontally and wishes to climb.
At the rear of the machine and forming part of its tail is a hinged
horizontal flap called the “elevator,” under the control of the pilot.
By giving this flap an upward tilt he causes the air to exert a
downward pressure on the tail of the machine, and hence the nose of the
machine is carried upward. While the inertia of the aeroplane tends to
carry it along the original path, its wings now present a greater angle
to the air, the lift is increased, and the machine rises. The reverse
of this operation will cause the machine to descend.

[Illustration: THE BED OF POTOMAC RIVER, AT WASHINGTON. From an
altitude of a few hundred or a few thousand feet, submarine features
are clearly revealed to great depths. Objects have thus been
photographed 45 feet under water. The shoals are submerged to a depth
of from 2 to 5 feet. In favorable weather, aerial photographs are
valuable in making hydrographic surveys. (_Photographed from the air by
Dr. W. T. Lee, U. S. Geological Survey._)]

A vertically hinged flap in the tail, acting on exactly the same
principle as the rudder of a ship, enables the pilot to turn
horizontally. Two or more small horizontal flaps, known as “ailerons,”
attached to the wings, are used to preserve the lateral balance of the
machine, and to give it the proper “bank,” or inclination, when making
a turn.

[Illustration: DRILLING WITH COMPRESSED AIR IN A COPPER MINE. The
drill also forces a stream of water into the hole to lay the dangerous
sulphur-bearing dust. (_Courtesy Sullivan Machinery Co._)]

[Illustration: LAUNCHING A WEATHER BUREAU KITE FROM THE “SENECA” DURING
THE INTERNATIONAL ICE PATROL, TO EXPLORE THE AIR OVER THE OCEAN.

(_Photograph, U. S. Weather Bureau._)]

With these few details in mind, we shall be prepared to consider, in a
general way, how the behavior of an aeroplane is affected by the wind
and other atmospheric phenomena.

With respect to wind there is an important difference between aircraft
and marine craft. Mere strength of wind is not dangerous to an
aeroplane, except when starting or landing. An aviator flying above the
clouds, with no landmarks in sight by which to gauge his movements,
is no more conscious of the actual wind at that level, provided it is
steady, than he is of the rotation of the earth on its axis. He feels
the wind produced by the motion of his machine through the air--the
so-called “relative wind”--but no other. The true wind may be a mere
zephyr, or a hurricane blowing 150 miles an hour; the effect is the
same on his machine, so far as he is able to observe. On the other
hand, a strong wind has a very different effect from a light one
upon the course of the aeroplane’s flight with respect to the ground
beneath. If a pilot, with no landmarks to guide him, steers by compass
for a certain point, and if there is a strong cross-wind of which he is
unaware, he will be carried far out of his course; a wind dead ahead
or astern will merely affect the speed of his flight, so that he will
arrive later or sooner at his destination than he expected.

One of the important problems of aeronautics, especially from the
commercial point of view, is to prevent aircraft from being driven
off their course by the wind when flying with no visible landmarks;
i. e., over clouds, fog, the ocean, or an unmapped country. When this
problem is solved, pilots will fly above the clouds much more commonly
than they do now. The winds at high levels are generally both steadier
and stronger than at low. The stronger wind is an advantage or a
disadvantage, according to whether it is blowing in the direction of
flight or the reverse; but as the winds at different levels generally
blow in different directions, a pilot who is independent of landmarks
can choose whatever level affords the winds most favorable for his
intended journey.

Over established air routes quite elaborate measures are now adopted
to keep pilots informed of the direction and speed of the wind at
different levels, so that they can make due allowance for this factor
in shaping their course. In clear weather this information is easily
obtained by sighting the drift of a pilot balloon with a theodolite,
or by observing in a specially designed graduated mirror or pair
of mirrors the drift of the smoke cloud from a shell fired by an
anti-aircraft gun and timed to burst at any desired altitude. In cloudy
weather the smoke trails can often be successfully observed through
small breaks in the clouds. When the sky is completely overcast, a
succession of shells is fired at definite short intervals of time and
the distances apart of the puffs of smoke and the direction of the
line in which they lie are determined from an aeroplane flying above
the spot. Another method, which was devised by the French military
meteorological service during the war, is to send up small balloons
loaded with bombs which burst after a certain time, the position of
each burst being determined by sound-ranging from the ground.

These methods of providing information concerning the winds at flying
levels have, however, their serious limitations, and aeronauts now look
hopefully to the perfection of the existing systems of “directional
wireless,” whereby the pilot will receive whenever desired, or at
regular intervals, a wireless signal from the terminus of his route or
some other known point, the direction from which the signal comes being
indicated by suitable apparatus on the aeroplane. Thus aided, he should
never deviate far from his course, unless he chooses to.

For long journeys, such as the crossing of the Atlantic, the air pilot
will naturally make use of all available information concerning the
great permanent or semipermanent wind systems of the earth, such as the
trade winds of the lower atmosphere, the antitrades above them, and
the fairly constant eastward drift of the atmosphere at high levels
in middle latitudes. The dividend-earning capacity of commercial
aircraft necessarily depends upon taking advantage of favorable
winds, while adverse winds may mean not only a loss of money but the
danger of prolonging a journey until the fuel supply is exhausted--a
serious predicament over the ocean and also over lands remote from
civilization. It is, however, a common error on the part of current
writers to overrate the constancy and reliability of the winds in
various parts of the world, and to lay too much stress on the value
of permanent wind charts. What the aeronaut needs especially to know
is the typical behavior of the winds with respect to the distribution
of barometric pressure, as shown by a weather map, including their
variations with altitude. The time will come when the information
necessary for plotting the winds at various levels will be flashed at
frequent intervals by high-powered radio stations to aerial navigators
in all parts of the world--a system that is already in its initial
stages, especially in Europe. A pilot making a long journey will thus
be able to lay his course so as to utilize the winds that will speed
him on his way. Even violent storms, such as the mariner seeks to
avoid, will be turned to advantage by the airman.

We have now to consider another aspect of wind that is of much more
interest to the airman than to the seaman, and that is the question
of “wind structure.” The layman usually thinks of a wind as a nearly
steady horizontal flow of air. Such winds exist, but they are
exceptional, especially in the lower levels of the atmosphere. A wind
is generally full of gusts and eddies, upcurrents and downcurrents,
and it is these eccentricities that gradually develop in the aviator
a sort of sixth sense--a “feel” for atmospheric fluctuations, that
enables him to adjust his machine instinctively to the forces tending
to disturb its equilibrium. He also learns by experience the conditions
under which irregularities of a pronounced character may be expected.
He becomes well acquainted with the great mound of air that drives his
machine upward when passing over a hill or mountain; with the eddy that
lurks in the lee of such an obstacle; with the downward tendency of the
air over lakes, rivers, swamps and forests.

“The air is so sensitive,” writes the late well-known British flyer,
Gustav Hamel, “that it is affected even by the color of large patches
of vegetation. Whether this be entirely due to the different
heat-radiating power of different colors it is impossible to say, but
invariably an aeroplane on passing from grass land to a field covered
with yellow flowers experiences a certain amount of air disturbances
only less noticeable than the inevitable bump experienced in passing
from green fields to ploughed land, or from ploughed land to meadow.”

When the wind is blowing, the air for at least a few hundred feet above
the ground is nearly always in a state of turmoil. This is partly due
to the friction of the moving fluid against the irregular surface of
the earth, and partly to the ascending and descending currents caused
by differences in temperature. The latter effect is illustrated in
the rapid rise of air over a bare sunlit plain and its fall over an
adjacent forest or body of water. Ascending currents are often made
visible by the formation of detached cumulus clouds, each of which
marks the summit of a rising column of moist air, while in the spaces
between the clouds the air is generally sinking. Measurements with
balloons have shown that vertical currents often attain speeds of 600
feet a minute or more, while the process of hail formation appears
to indicate that in thunderstorm clouds there are violent uprushes
amounting to 2,000 or 2,500 feet a minute, and possibly much more. The
descending air current between clouds is sometimes so strong that an
aeroplane cannot force its way up through it.

[Illustration: THE FLOW OF AIR OVER TWO RIDGES

(_After Dr. Franz Linke._)

Notice the eddy in the valley to the leeward of the first ridge]

[Illustration: A SHELTERED LANDING PLACE MAY BE DANGEROUS

(_After Dr. Franz Linke._)

A landing place surrounded by trees is dangerous in windy weather on
account of the air waves formed between the moving air above and the
calm air below.]

[Illustration: AIR WAVES NEAR THE EARTH’S SURFACE

The waves are made visible by smoke]

The turbulence of the lower air--a phenomenon that adds so much to
the difficulties of starting and landing--extends to various heights,
depending especially upon the strength of the wind. A rough rule,
evolved by the Zeppelin pilots before the war, was to expect turbulent
conditions up to an altitude equal to from ten to twenty times the
force of the wind in meters per second. Thus, for a wind of 10 meters
per second, the turbulent layer would be from 100 to 200 meters thick.
A good picture of the atmospheric ups and downs encountered by the
airman when flying low is furnished by the behavior of the smoke from
a factory chimney with a moderate wind blowing, forming smoke waves.

[Illustration: THE WIND’S AUTOGRAPH ON A GUSTY DAY, RECORDED WITH A
PRESSURE-TUBE ANEMOMETER

The vertical lines are hour lines and the horizontal lines show the
force of the wind in miles an hour and also in pounds a square foot.]

These disturbances give rise to the very marked fluctuations in the
force of the wind known as gusts. There are certain forms of anemometer
especially designed to record the gustiness of the wind. A record of
the wind’s force is traced by a pen on a moving strip of paper, and the
“anemogram” thus obtained shows a continuous series of irregularities,
the extent of which increases with the strength of the wind. The puffs
and lulls often alternate at intervals of a few seconds or less, and
the actual force of the wind at a given instant may be many times
greater than its average force for, say, five minutes. An ordinary
anemometer does not indicate these rapid fluctuations, but merely shows
the time required for a mile of wind to flow past the instrument. Thus
when such an instrument tells us that the wind is blowing at the rate
of 40 miles an hour, it may actually be varying between 20 and 60
miles an hour, or between even wider limits.

Since the matter became of practical importance on account of the
needs of aviation, many interesting studies have been made of the
effects of different kinds of topography upon the overlying air
currents. A striking example of the eccentric winds that sometimes
prevail in mountain valleys has been described by Mr. B. M. Varney,
of the University of California, in the “Monthly Weather Review.”
From the summit of a steep cliff about 1,100 feet above the floor of
Yosemite Valley the writer launched broad sheets of tissue paper, and,
with the aid of powerful binoculars, followed their flight as they
were carried in huge spirals, thousands of feet in diameter, finally
disappearing beyond the mountains on the opposite side of the valley.
The accompanying sketch shows the path of one of these papers. From its
starting point at _A_ until it passed behind the summit of Liberty Cap
(_B_), more than a mile distant, the paper was watched for 7 minutes.
The top of Liberty Cap is some 1,600 feet above the point at which the
flight began. This sketch visualizes one of the ticklish problems that
will some day confront the pilot of a sight-seeing or mail-carrying
aeroplane in the Yosemite National Park.

[Illustration: AIR CURRENTS IN YOSEMITE VALLEY

(_Sketched by B. M. Varney._)

The flight of a sheet of paper across the valley.]

Although, on an average, the air is much steadier at high levels than
near the ground, very unsteady currents are sometimes found at all
altitudes attainable by aircraft. Thunderclouds, thousands of feet
above the earth, are always the seat of violent turmoil, but such
clouds can, as a rule, be avoided by the airman. When a stratum of air
glides over another differing sharply from it in density--and distinct
strata of this sort are not uncommon in the atmosphere--friction
between the strata sets up waves like those produced in water by wind
blowing over it. If the two streams are moving in the same direction,
but at different speeds, the waves are long and regular; when they are
more or less crossed, the waves are short and choppy. The moisture
at the crests of these waves may be cooled to such an extent as to
condense into visible clouds, arranged in long continuous rolls or rows
of detached patches; forms frequently assumed by cirro-cumulus and
alto-cumulus. More often, however, the waves of air remain invisible,
because the conditions of moisture and temperature are not right for
the production of cloud.

Recalling, now, what has been said above about the way in which the
lift of an aeroplane varies with the angle at which the wings meet
the air and also with the speed of the machine relative to the air,
it will be easy to understand some of the difficulties experienced in
maintaining one’s equilibrium when flying in a turbulent atmosphere.
Waves, eddies, vertical currents and other features of wind structure
cause abrupt changes in the attitude and the speed of the machine with
respect to the air stream. The sudden increases and decreases of lift
thus produced have much the same effect upon the machine as if it
were running over a solid obstacle on the one hand or plunging into
a vacuous space in the atmosphere on the other, and hence are aptly
described by aviators as “bumps” and “holes in the air,” respectively.
The latter term, which seems to have become firmly rooted in all
languages (French, _trou d’air_; German, _Luftloch_; etc.), has had
the unfortunate effect of keeping alive in the public mind the idea
that the aviator occasionally runs into a vacuum or semivacuum, such
as could not exist in the atmosphere. (The nearest approach to such a
thing is the rarefaction in the core of a tornado or waterspout, due to
the enormous centrifugal force of the vortex; something that no aviator
has yet encountered.)

To make matters worse, different parts of the sustaining surface of
the machine may receive different impulses. One wing, for example, may
graze a violent uprush of air not encountered by the other, giving
the aeroplane a tilt to one side, or the tail of the machine may be
driven in one direction and the nose in the other. Again, the whole
machine may suddenly enter an air current of quite different speed and
direction from the one in which it has been flying. To take an extreme
case, it may run into a stream of air flowing just as fast, and in
the same direction, as the machine itself, with the result that the
_relative_ wind becomes zero, and the machine, deprived of all lift,
drops like a stone until it acquires a velocity with respect to its new
environment.

When such conditions prevail, the pilot is kept busy with his
“controls”; now moving his elevator to adjust his fore-and-aft balance,
and now his ailerons to set him on an even keel laterally, and
occasionally turning his rudder to offset the effects of horizontal
gusts. The elevator and the ailerons are worked with a single lever,
colloquially called the “joy-stick,” and the rudder with a bar which
the pilot operates with his feet. Ordinary adjustments of this kind
are performed automatically by the trained aviator, but violent
disturbances call for the exercise of skill and judgment. Generally
speaking, no amount of atmospheric turbulence causes any serious
trouble to the trained pilot, except when he is flying close to the
ground, as in starting and landing.

Before we leave the subject of wind it will be well to emphasize once
more the fact, which the average layman has difficulty in grasping,
that the only movements of the air that affect the safety and comfort
of flight are the movements relative to the machine, and not those
relative to the ground. To the aviator, when he is once clear of the
ground, a steady wind of any speed is merely a mass of calm air. Hence
an aviator will sometimes have perfectly smooth flying when the wind,
as measured on the earth, is blowing 40 or 50 miles an hour; and again
he will describe the air as rough and bumpy when flags are hanging
limp from their staffs and dwellers on _terra firma_ declare that not
a breath of air is stirring. In the early days of flying aviators
themselves were afraid of a strong wind. Thus Wilbur Wright, during
his pioneer exhibition flights in France, would never go up unless the
smoke from his cigarette rose in a straight line, and until about the
end of 1909 no aviator attempted to fly in a wind of 20 miles an hour.

At the present time the only atmospheric condition that seriously
hampers flying is fog or low cloud. An aviator flying in a fog or cloud
is not only liable to wander far from his course, on account of the
unknown leeway of his machine, but he is often in great doubt as to his
proximity to the ground. One of the curious effects of such a situation
is that the airman loses his sense of the vertical. On land our sense
of up and down is determined by the force of gravity, pulling us toward
the earth. When riding in a terrestrial vehicle, we are conscious of
other pushes and pulls; such, for example, as the jolt that pitches
us forward when a train stops suddenly, or the outward thrust that we
feel when swinging around a curve. Again, in descending in a lift we
seem to lose weight, as if gravity had suddenly grown weaker. On earth
all such impressions are corrected by the sight of objects around us;
but the aviator enveloped in mist has no such guides, and he often
becomes quite confused about the direction of the ground. A turn, which
involves banking, increases his confusion. Eventually he may be flying
almost upside down without being aware of the fact. Professor Melville
Jones, who has been through such experiences, says of the pilot’s
confusion:

“His first indication that something is wrong is, as a rule, either
an increase or a decrease of speed that is not counteracted by the
accustomed movements of the controls. A period of wild suspense and
utter bewilderment now follows, during which the pilot makes violent
efforts to recover control, but without success. The next thing that he
realizes, if he realizes anything at all, is that he is either on his
back or spinning, and the next thing he knows is that he is out of the
clouds with the earth standing up at a ridiculous angle and spinning
round like a drunken dinner plate. Happy is he that has plenty of air
room under these circumstances.”

Spirit-levels and similar instruments are affected by the same
disturbances that mislead the pilot in his estimation of the vertical;
but fortunately there are certain other devices, due to the exigencies
of the war, during which cloud flying was a part of the tactics of the
military aviator, which have virtually solved this problem, though
their use has not yet become general.

The outstanding difficulty of a fog is the problem of landing. In the
case of a forced landing, at a distance from a regular landing-ground,
the pilot must simply trust to luck. He may descend in the water or the
treetops, or on rough ground that will wreck his machine, but he has no
choice. The only solution of this difficulty is the installation of a
reserve engine, or some other expedient that will obviate the necessity
of forced landings. The task of finding a landing ground in a fog and
descending to it in safety will, in the near future, be comparatively
simple. Most fogs, though by no means all, are so shallow that it is
possible to tether a kite-balloon so that it will float above the fog
and indicate the position of the aerial harbor. Several such balloons,
flying tandem, would afford sufficient lift to support a series of
electric lanterns along the cable, for use at night. Searchlights and
“star shells” have been employed for the same purpose. Directional
wireless and the wireless telephone seem likely, however, to be the
chief dependence of the future aeronaut seeking port in a fog. These
devices will also be the means of averting collisions in a fog or cloud
along crowded airways, and especially in the congestion that will
prevail in the vicinity of important air ports. Last but not least,
the artificial dispersion of fog by means of electrical discharges,
although still in the experimental stage, holds out possibilities
of being the ultimate solution of the fog problem, not only for the
aeronaut, but also for the mariner, the railway manager, and everybody
else who is incommoded by a misty atmosphere.

Even when he is not flying in clouds or fog the aviator by no means
always enjoys a clear view of distant objects. A slight haze impairs
visibility, while a heavy rainstorm or snowstorm may obstruct the
aeronaut’s view as badly as a fog.

Of the meteorological elements that affect aeronautics, other than
those we have mentioned, the most important is the density of the
atmosphere--generally expressed in terms of barometric pressure. The
air diminishes in density upward, and the rarefied atmosphere of high
levels has several effects on aircraft. Its decreased buoyancy imposes
a limit upon the ascent of balloons; its decreased resistance makes
it necessary for an aeroplane to fly at greater speed in order to get
the same lift; it diminishes the power of gasoline engines, on account
of the reduced supply of air; and it has various unpleasant and even
dangerous effects on the aeronaut, similar to “mountain sickness.” The
level that a given aeroplane cannot exceed owing to the combined effect
of reduced lift and reduced engine power is known as its “ceiling.”
Different types of aeroplane have very different ceilings.

At great altitudes the air is always very cold, summer and winter.
The low temperature may interfere with the efficient working of the
engine, and it is, of course, a source of discomfort to the pilot. The
formation of ice and heavy deposits of snow lead to inconveniences
in both aeroplanes and airships. The pelting of hail is sometimes a
painful experience for aeronauts. Lastly, lightning has hitherto left
aviators unscathed, but has caused numerous disasters among balloonists.

The recent rapid development of aeronautics has laid a heavy burden of
additional labor upon the meteorological services of the world, and
is producing something like a revolution in their methods. The history
of these changes is interesting. From the beginning of the twentieth
century until a few years before the World War meteorologists were
engaged in a great campaign of upper-air research, utilizing kites,
captive balloons, pilot balloons, and sounding balloons to measure
the winds, temperature, humidity and pressure at various levels in
the atmosphere. In other words, aeronautical methods were employed in
the service of meteorology, but the investigators hardly entertained
the idea of reversing the relation and making meteorology the
handmaiden of aeronautics. The point of view prevailing in those days
is well indicated by the fact that the organization that had charge
of the upper-air explorations throughout the world was known as the
“International Commission for Scientific Aeronautics,” a name that it
bore until the year 1919.

The plan for providing regular weather reports for the benefit
of aeronauts began with some small-scale enterprises in Germany
about 1909. In the summer of that year Dr. Franz Linke organized a
storm-warning service in connection with the International Aeronautical
Exposition at Frankfort, and at the beginning of the year 1911 an
aeronautical weather bureau for the whole of Germany was established,
with headquarters at the Observatory of Lindenberg. Shortly before the
war a similar undertaking was launched in Italy, under Dr. Matteucci,
whose service was the first one in the world to publish daily charts,
based on telegraphic reports, of the winds at various levels over an
entire country.

During the war the regular meteorological services of the belligerent
countries and the meteorological units attached to the armies and
navies maintained an almost continuous service of weather information
for the great fleets of fighting aircraft. Bulletins, distributed
chiefly by wireless telegraphy, supplied particulars of the current
and prospective winds at the flying levels, the prevalence of fog,
the degree of visibility, etc. New telegraphic weather codes, far
more elaborate than those in use before the war, were devised for
transmitting such information, and the whole business of observing and
reporting weather became immensely more arduous than it had been in the
days when the only interests served by practical meteorology were those
of the land and the water.

Since the close of hostilities great efforts have been made to maintain
these new operations of the meteorological establishments at something
like the level attained during the war. The task is, however, beset
with difficulties, on account of the great expense involved. It is
being accomplished with different degrees of success in different
countries.

CHAPTER XIX

MILITARY METEOROLOGY

One of the most astonishing paradoxes connected with the misapplication
of human brains and energy glorified with the name of the “art of war”
is this--that, while weather has always played an important part, and
often a decisive one, in military operations, no attempt was ever made
until a few years ago to include meteorology in the purview of military
science or to utilize the services of meteorologists at the battle
front.

The most casual survey of the history of warfare reveals the fact that
atmospheric conditions rank high among the “controls” of fighting. From
a military point of view, weather and climate bear a certain analogy to
topography. They are a part of the physical environment with which a
commander has to reckon. Weather, however, differs from topography in
the fact that it is subject to rapid changes, and is therefore doubly
worthy of attention on the part of an army, which must not only take
account of the weather as observed and in progress, but must also, as
far as possible, anticipate that which is to follow.

Everybody will recall the ruin that overtook the French army in Russia
in 1812 on account of untoward weather conditions, but it is less
well known that Napoleon, with his usual sagacity, obtained from his
scientific advisers a report on the Russian climate before he planned
his campaign; that the winter set in much earlier than usual in that
fatal year; and, most interesting of all, that it was actually a brief
period of thawing weather, rather than the intense cold that preceded
and followed it, which, by turning the roads into bogs and breaking up
the ice in the Beresina, brought about the culminating disaster.

Another fateful spell of weather ushered in the battle of Waterloo.
It is described in a well-known passage of “Les Misérables,” which
contains enough truth mingled with hyperbole to be worth quoting:

“S’il n’avait pas plu dans la nuit du 17 au 18 janvier, 1815, l’avenir
de l’Europe était changé. Quelques gouttes de plus ou de moins out
fait pencher Napoléon. Pour que Waterloo fût la fin d’Austerlitz, la
Providence n’a eu besoin que d’un peu de pluie, et un nuage traversant
le ciel à contre-sens de la saison a suffi pour l’écroulement d’un
monde.”

The rains and floods that led to the annihilation of the Roman legions
under Varus in A. D. 9 and the great tempests that helped English
seamen defeat the Spanish Armada furnish additional well-known examples
of the immense importance of weather as a factor in warfare. We need
not, however, look farther back than to the recent world conflict
to find similar examples in profusion. Leaving out of consideration
the indirect effects of the weather upon the progress of the war as
exercised through its control of crops, transportation, and other
features in the economic life of the belligerent and neutral nations,
we need only examine war-time newspapers to see how the armies
themselves were helped or harassed by meteorological conditions at
every turn. The war was a great popular teacher of climatography,
just as it was of geography. The drenching misery of Flemish winters,
as formidable to the soldiers in the trenches as the bullets of the
enemy, became as familiar to the present generation of Americans as did
somewhat similar conditions in Virginia to Americans of the Civil War
period.

The British campaigns in Mesopotamia were as much a conflict with
climate as with human foes. Marches were made when the temperature
stood at 110 degrees Fahrenheit and over. The temperature in the
hospital tents is said to have reached 130 degrees. The disaster
at Kut-el-Amara was due to the rains and floods that prevented
reenforcements from reaching the beleaguered garrison. The failure of
the Dardanelles expedition was partly due to the fact that the extreme
dryness of the country was not realized--as it would have been if
the War Office had called climatologists into council--and totally
inadequate provision was made for the water supply.

The new engines of war brought forth by the recent struggle were
peculiarly susceptible to the effects of weather. The larger guns
and heavy motor trucks were difficult to move over muddy roads. The
aircraft, though they managed to fly in all kinds of weather, suffered
innumerable disasters for which atmospheric conditions--chiefly storms
and fog--were responsible, and their operations were conspicuously
affected by favorable and unfavorable winds. Shells were fired to
unprecedented heights, and their trajectories were modified by unknown
conditions in the upper air. Last but not least, the use of poisonous
gases, especially in the period before gas clouds were largely replaced
by gas shells, was dependent upon the occurrence of appropriate winds;
and a slight miscalculation in this respect sometimes brought disaster
to the troops using the gas.

It is not surprising that professional meteorologists played a part in
the World War, but it is difficult to understand why meteorological
units were not attached to all armies, at least when on active service,
several decades before the year 1914. Meteorologists did, indeed, take
a hand in one earlier conflict, but not as enrolled soldiers. During
the Spanish-American War a special service was organized by the United
States Weather Bureau to protect the American fleet in southern waters
from unpleasant surprises in the shape of West India hurricanes. In
the summer of 1898 a chain of observation stations was established
by the Bureau around the Caribbean Sea. The service then inaugurated
in consequence of the exigencies of war proved so valuable to
shipping in time of peace that it has continued to operate, with some
intermissions, down to the present day.

When the World War broke out, the only country that immediately put
meteorologists, as such, into the field was Germany. The Germans were
fortunate in having a far greater number of trained meteorologists at
their disposal than had their enemies. There were chairs of meteorology
in several German universities and high schools, and the numerous
meteorological observatories and institutes of the Empire had provided
occupation for a large amount of professional talent in this line. One
of the first acts of the army that invaded Belgium was to establish an
aerological service in that country.

The Entente countries were slow in adding meteorological units to their
armies, but their civilian meteorological services were utilized to
the utmost for military purposes from the beginning of the war. They
at first worked under difficulties arising from the cessation of the
customary weather reports from central Europe, but, to offset this
disadvantage, the weather map was expanded in other directions, the
number of daily hours of observation was increased, and eventually the
forecasters in London and Paris acquired much better facilities for
making their predictions than they had enjoyed in time of peace. The
supply of weather information to the public was suspended, and great
precautions were taken to prevent the reports of the Allied services
from being utilized by the enemy. The German meteorologists were
seriously hampered by the lack of reports from the westward. It has
been asserted that such reports were sometimes obtained by radio from
submarines stationed off the coast of Ireland, but such a service, if
it existed, must have been fragmentary and unsatisfactory. That the
Germans made many mistakes in their attempts to infer the atmospheric
conditions over the British Isles from the limited weather map at their
disposal is proved by the fact that their airships frequently crossed
the Channel when, with an ampler knowledge of impending weather, they
would certainly have remained at home. Several Zeppelins came to grief
in the course of these ill-timed raids. One of the interesting routine
duties of the British Meteorological Office during the war was to draw
the weather map for a given moment as the Germans would probably draw
it, with their curtailed set of telegraphic reports, and then predict
the German prediction!

In the spring of 1915 a small meteorological section was organised in
the British Army, and attached to the Royal Engineers. This force was
afterward enlarged, and provided units for service on several battle
fronts. The British also developed a naval meteorological service,
which had existed in embryo before the war, and, eventually, a special
meteorological service for the Royal Air Force. Analogous services were
organized by the French and the Italians.

The United States Army and the United States Navy both established
meteorological services not long after this country entered the war.
The former was attached to the Signal Corps, and was partly officered
and recruited from the Weather Bureau. A training school for army
meteorologists was opened at College Station, Texas. Upward of 300
men were given instruction in this school, and most of them were sent
overseas. The naval meteorological service was headed by the director
of Blue Hill Observatory, and the junior officers received special
training at that institution.

The varied activities carried on by these war-time units were so
different from the traditional duties of meteorologists that they may
be said to mark the advent of a new branch of applied science--Military
Meteorology. They were, moreover, as we shall see, extremely fruitful
of effects upon the science of meteorology in general.

In the principal battle zones the military weather men maintained a
dense network of observation stations, the reports from which, combined
with those received from the regular peace-time weather stations of the
Allied and neutral countries, enabled the forecasters at headquarters
to keep closely in touch with atmospheric changes. Observations of
both surface and upper-air conditions were made at frequent intervals,
and radiotelegraphy was largely used to insure prompt transmission
of the reports. In general, weather maps were drawn four times a day.
Information was distributed locally to the fighting units by telephone
and otherwise.

The vast fleet of aircraft called into being by the war would, of
itself, have imposed upon the military meteorologists the necessity of
paying a great amount of attention to the upper air. Pilot balloons
were sent up so frequently and at so many points that the aviators
generally knew just what winds they would encounter aloft. Special
arrangements were made to follow the progress across the country of the
thundersqualls which constituted a serious danger to the “sausages,” or
observation balloons, as well as to aeroplanes on the ground, and to
hangars.

There was, however, another urgent reason for keeping a close watch
of the winds and other atmospheric conditions at various levels above
the earth’s surface. Experience acquired early in the war proved
that old-fashioned methods of correcting the aim of artillery for
meteorological disturbances were extremely inadequate for modern
guns, the projectiles of which rise to altitudes of from 10,000 to
20,000 feet and encounter conditions quite different from those
prevailing at the surface. The flight of a projectile is affected
by the force and direction of the wind, and the density of the air
through which it passes. Some modern projectiles remain in the air as
long as 70 seconds, and a moderate wind blowing across the path of
such a projectile may easily cause it to fall half a mile away from
the point at which it would strike if fired in still air. One of the
routine duties of the army weather service was to observe the winds
and compute the air-densities at different heights wherever such
information was required by the artillery. In order to facilitate
the application of such data by the gunners ingenious methods were
developed for computing what is known as the “ballistic wind.” This is
a fictitious wind which, if affecting the projectile throughout its
flight, would produce the same total deflective effect and effect on
range as the various winds that the projectile actually encounters.

Meteorological observations were also of great importance in connection
with the new process of locating distant guns known as “sound-ranging.”
This process consists, briefly, in determining the exact instant of
arrival at several points of the sound waves propagated through the
air from the gun that is being located. If sound traveled at a uniform
speed, these observations would show the exact distance of each of the
observing points from the gun, and a simple geometrical construction
would indicate the position of the latter. The speed of sound waves
in the air is, however, affected by both wind and temperature.
Accordingly, allowance had to be made for these varying factors, and
the necessary data were supplied by the meteorological units.

The observation and prediction of winds favoring the use of poisonous
gases by friend or foe was one of the most delicate tasks allotted
to the army meteorologists. The flow of such gases is determined by
the winds close to the surface of the earth, and these are greatly
affected by topography. Local air currents controlled by the slope
of the ground were especially utilized for gas attacks. Strong winds
were unfavorable, because they quickly dissipated the gas cloud. The
meteorologists not only advised their own troops when to use gas, but
also gave warning when the atmospheric conditions were such that gas
was likely to be used by the enemy. The use of gas shells was less
dependent for its success upon the wind than the liberation of gas
clouds, but even when shells were used the wind and weather at the
objective point were factors of importance.

The exigencies of warfare developed several new features of
meteorological practice, the utility of which did not cease with the
war. Thus it became customary to measure the degree of “visibility”
of distant objects, for the benefit of aviators and gunners, and
this element was included in the routine weather reports. Scales of
visibility, ranging from “very bad” to “excellent,” etc., were adopted,
and eventually certain forms of apparatus (“visibility meters”) were
devised for getting fairly precise measurements of this weather factor.

Another novel practice that deserves to be perpetuated was the plan
adopted by the military forecasters of adding to their predictions
a statement as to their probable accuracy; this was expressed on
a numerical scale of “odds,” instead of by use of the vague terms
“probably” and “possibly,” which have generally served the purpose of
the dubious forecaster.

The war brought about many improvements in the instruments and
methods used in sounding the upper air; and the intensive campaign
of pilot-balloon observations carried out at the military stations
provided a body of data for study quite unparalleled in the history of
meteorology.

Lastly, the war revolutionized weather telegraphy in Europe. Before
the war the European forecasters were hampered by exasperating delays
in the collection of reports over the telegraph lines, especially in
the international exchange of observations. Wireless telegraphy had
been extensively used for gathering reports from vessels and supplying
vessels with forecasts, but not for the interchange of meteorological
information on land. The war changed all this. Radiotelegraphic weather
messages became the rule, and the advantages of the new system were
so obvious that the tendency has been to retain it as far as possible
since the war.

CHAPTER XX

MEDICAL AND PHYSIOLOGICAL METEOROLOGY

The starting point in any study of the physiological effects of weather
and climate upon humanity is the remarkable fact that, on the hottest
days of summer and the coldest of winter, in tropical deserts and amid
polar snows, the temperature within the body of a healthy man remains
constant to a fraction of a degree. There are slight temperature
differences between different parts of the body; there is a periodic
daily variation of about half a degree; and there are other slight
changes, due to eating and exercise; but an internal temperature
of about 98.6 degrees F. is maintained with little or no regard to
fluctuations in the temperature of the air.

The body has often been compared to a building in which the temperature
is regulated by a thermostat, but the comparison is not exact. The
thermostat controls the temperature merely by regulating the combustion
of fuel; and with the advent of mild weather we let the fires go out
altogether. In the body the fires are always burning, the briskness
with which they burn--or, to drop the metaphor, the rate at which
bodily heat is generated--depending, above all, upon muscular activity,
but also upon other causes. It is true that we possess a nervous
mechanism, analogous to the thermostat, which tends to adjust the
production of animal heat in such a manner as to offset the cooling
effect of our environment; but this mechanism appears to be less
important in maintaining our constant temperature than another, which
regulates the loss of heat from the body. According to M. J. Rosenau:

“Heat is lost from the body chiefly in two ways; (1) by _heat
transfer_, or loss by radiation, conduction, and convection; (2) by
_evaporation_, chiefly by the evaporation of the water of perspiration.
Pettenkofer and Voit estimated the loss of water by the lungs at
286 grams, and from the skin at from 500 to 1,700 grams daily. This
will give some idea of the effects here concerned. The loss by heat
transfer diminishes as the temperature of the surrounding air rises.
The temperature of the body would rise when the atmospheric temperature
goes above 70 degrees F. were not perspiration then secreted. So long
as the perspiration can evaporate freely the heat production and heat
loss are balanced. With a high humidity evaporation is lessened and the
balance is maintained by rushing blood to the skin, which causes an
elevation of the temperature of the surface, and thus the loss of heat
by radiation, conduction, and convection is facilitated.”

Human sensations of temperature are paradoxical. We talk of being “hot”
and “cold,” as if we belonged to the class of cold-blooded animals--the
fishes and the reptiles--that actually undergo great variations of
temperature, with variations in the temperature of their environment.
We hear people say, for example, that they are most comfortable at a
temperature of 65; yet we know that their temperature is always 98½,
except just at the surface of the body.

The human body is, in fact, a poor thermometer. Our sensations do not
register the temperature of the air, but they do, in a way, register
the cooling power of the air, which depends upon temperature, humidity,
and air movement, and they register, especially, changes in this
cooling power, for within certain limits the body soon adapts itself
to a constant rate of cooling, so as to lose any impression of heat or
cold. When a steady outflow of heat from the body has been set up and
the external cooling power is suddenly increased, we become conscious
of a difference between the temperature at the surface of the body
and the “blood temperature” beneath. The action of the nerves at the
surface and the nerves underneath, under these circumstances, has been
compared to that of a thermo-junction, in which an electric current is
produced by differences of temperature. The rate of evaporation from
the skin, also, has a marked effect upon our sensations of comfort and
discomfort.

The common thermometer was long ago discredited as a means of measuring
atmospheric comfort. Then, for a time, the wet-bulb thermometer had its
day, and its indications were once published on a large scale in this
country as representing the “sensible temperature,” or temperature that
we actually feel. The wet-bulb thermometer is cooled by evaporation
below the air temperature, except when the air is saturated with
moisture, and may therefore give a rough indication of the temperature
acquired by the skin when moistened with perspiration. The temperature
of the skin is not, however, an accurate indication of our feelings
of heat or cold, nor is it a satisfactory guide to the physiological
effects of atmospheric conditions.

Several instruments have been devised for the purpose of measuring the
cooling power of the air, to which the bodily mechanism must respond
in order to maintain a uniform temperature within. One of these was
invented nearly half a century ago by J. W. Osborne. A porous cylinder
was filled with warm water, and an agitator, driven by clockwork, kept
the water in the cylinder at uniform temperature at any given moment.
The rate at which heat was lost from the wet surface of the cylinder
was determined by a thermometer, having its bulb immersed in the water,
and a stop watch. A different plan was adopted by A. Piche, in an
instrument which he called the _deperditometer_, and which was supposed
to imitate more closely the behavior of the body. A porous vessel is
filled with water, the temperature of which is kept constantly at
“blood heat” (98.6 degrees F.) by a gas jet provided with an automatic
regulator. The amount of gas burned in a given time is then supposed to
measure the cooling power of the atmosphere as it affects humanity. J.
R. Milne’s _psuchrainometer_ is constructed on the same principle, but
heat is supplied and measured electrically.

Among many other instruments of this class, one that now enjoys special
favor is the _katathermometer_, devised by Prof. Leonard Hill, in
England. This consists of a pair of large-bulbed spirit thermometers,
one of which has its bulb covered with fine cotton mesh. To use the
instrument, the bulbs are immersed in water at about 150 degrees
F. until the spirit rises to the top of the thermometer tubes. The
excess of water is then jerked off the wet bulb, and the other bulb
is dried. The instruments are finally suspended in the air, and the
rate of cooling from 110 to 100 degrees, or from 100 to 90 degrees,
is taken with a stop watch. The dry-bulb measurements are supposed to
show how fast the human body loses heat at its surface by radiation
and convection, while the wet-bulb measurements also take account of
evaporation.

In order to connect the readings of this device with human sensations,
Hill and his collaborators have used the instrument under a great
variety of atmospheric conditions, both indoors and out, and compared
the readings with independent estimates of comfort and discomfort. On
an ideal summer day the “wet kata” fell from 110 to 100 in 25 seconds,
and the “dry kata” in 85 seconds. Indoors at the seaside in summer,
under comfortable conditions, the readings were 50 seconds and 140
seconds, respectively. A large number of other readings, taken under
different conditions in various parts of the word, have been published.
The katathermometer is now used in both Great Britain and the United
States in the study of ventilation problems, and has acquired a rather
extensive literature. According to its inventor, “the heating and
ventilation of rooms should be arranged so that the wet-bulb falls from
100 to 90 degrees in about one minute, and the dry-bulb in about three
minutes.”

[Illustration: A WEATHER BUREAU KIOSK, IN UNION SQUARE, SAN FRANCISCO.

(_Photograph, U. S. Weather Bureau._)]

[Illustration: THE UNITED STATES WEATHER BUREAU STATION, OBSERVATORY
TYPE, AT PEORIA, ILLINOIS. (_Photograph, U. S. Weather Bureau._)]

Regardless of the merits of these particular instruments, it is
certain that the cooling power of the air--which is quite a different
thing from the temperature of the air--is a very important factor in
determining our comfort and our health. Within certain limits the body
can easily adjust itself to changes in the cooling power of the air;
within wider limits the adjustment is effected with difficulty, and we
experience discomfort and possibly suffer in health; and finally
there are extreme conditions, in either direction, to which adjustment
is not possible; the internal temperature is then either lowered or
raised, as the case may be, and a comparatively small change of this
sort is fatal; i. e., death results by chilling or by heat stroke.

  Photo U. S. Weather Bureau

THE CENTRAL OFFICE OF THE UNITED STATES WEATHER BUREAU IN WASHINGTON]

One interesting result of recent inquiries on this subject is the
discovery that the bad effects of crowded, “stuffy” rooms are not
generally due to impurities in the air, but to heat, humidity, and
especially lack of air movement. It seems to be now demonstrated
that there is no such thing as “crowd-poisoning,” and that the
bad smells of confined places are no indication that the air is
deleterious. Professor Hill, who has done more than anybody else to
upset traditional ideas with regard to ventilation, tells us that
“the deaths in the Black Hole of Calcutta, the depression, headache,
etc., experienced in close rooms are alike due to heat stagnation; the
victims of the Black Hole died of heat stroke.” Most recent writers
on physiology also discredit the time-honored methods of testing the
purity of the air by measuring the percentage of carbon dioxide it
contains. The amount of this gas normally present in the free air is
about three-hundredths of one per cent, but experiments have shown
that thirty times this amount--a percentage higher than is found in
the worst ventilated rooms--may be breathed for hours together without
detrimental effects. A further departure from old-fashioned views
is seen in the assertion of recent authorities that a deficiency
of oxygen, unless far more pronounced than ever actually occurs in
buildings, mines, etc., where the supply of this gas has been the
subject of so much solicitude, has no physiological significance
whatever. In support of this assertion it is pointed out that at
mountain health resorts the concentration of oxygen out-of-doors is
much less than that found in the worst ventilated rooms at sea-level.
In mines an ample supply of oxygen may be positively dangerous, as
favoring the occurrence of explosions. These were rare before the
enactment of laws requiring a high percentage of oxygen in mine air.

[Illustration: HILL’S KATATHERMOMETER]

Excessive dryness of the skin, which is a common cause of discomfort,
is not very closely related to the humidity of the air. “In winter,”
says Hill, “if there be a wind the rate of evaporation is so
accelerated that the skin feels dry, because in order to check the
loss of body heat the sweat glands are inactive and the blood vessels
of the chilled skin are constricted.” There has been a great deal of
discussion about the dry air of American buildings in winter, and
startling figures have been adduced to show that the air of such
buildings is dryer than that of deserts. So far as measurements of
relative humidity go, this is perfectly true; but, as Dr. G. T.
Palmer, of the New York State Commission on Ventilation, has pointed
out, there is an important difference between dryness and “dryingness.”
The latter depends upon the movement of the air, as well as the
relative humidity. The circulation of the air in a desert is generally
much more active than that of the air in a building with the windows
shut, and therefore much more conducive to rapid evaporation. There are
systems of ventilation in which the air is kept in steady and rapid
motion, and it is probably only in such cases that the air of our
heated houses can be compared to that of a desert. From the European
point of view American buildings are notoriously overheated, but this
is probably due to the fact that our hot summers--much hotter than
those of Europe--have adapted us to a tropical climate.

It is natural to inquire whether the atmospheric conditions that
affect the comfort of man do not also exercise a marked influence
upon his muscular efficiency and his mental powers. This question has
been answered in the affirmative by a number of ingenious writers,
who have sought to establish definite quantitative relations between
certain states of the atmosphere and the output of work in factories,
the grades attained by school children, etc. Thus, Dr. Ellsworth
Huntington, a well-known worker in this field, declares that the most
favorable daily mean temperature for mental activity (the temperature
being measured out-of-doors) is about 40 degrees F., and for physical
activity about 60 degrees F. Contrary to the common opinion, he holds
that our general efficiency is at low ebb in midwinter and fairly high
in summer. Variability in temperature, within certain limits, he finds
to be stimulating; equable temperature the reverse. He has drawn
charts showing the distribution of what he calls “climatic energy”--i.
e., the combination of certain weather factors supposed to control
human efficiency--throughout the world, and other charts showing a
more or less similar distribution of “civilization.” He has also made
an ambitious attempt to interpret the history of mankind in terms of
weather and climate.

Another fruitful worker along similar lines is Dr. Griffith Taylor,
of Australia, who has made interesting studies of the control of
settlement in his own country and elsewhere by temperature and
humidity, and has introduced some novel graphic methods (“climographs”)
for comparing climates with respect to their effects on humanity.

There has, in short, arisen a new school of climatologists whose aim
is to develop exact mathematical formulæ whereby we shall be able
to adjust the economic arrangements of mankind on an intelligent
basis as regards climate. The success of their efforts is a question
for the future to decide, but there is no doubt that their work is
profoundly suggestive. These undertakings, it may be noted, bear a
striking analogy to those of the present generation of agricultural
meteorologists, who are applying climatic statistics to the problem of
selecting crops and to the improvement of agricultural methods.

A certain number of specialists are engaged in studying the
physiological effects of sunlight and other special kinds of solar
radiation, the distribution of which varies greatly from place to
place and from time to time, especially on account of differences in
the selective absorption of such rays by the atmosphere. The chemical
action of sunshine that causes sunburn--even at very low temperatures,
as, for example, on high mountains--may have far-reaching effects on
the human organism (as it certainly has on plants), and there is great
need of collecting more data of “photochemical climate” than we now
possess, in order that this subject may be thoroughly investigated. One
of the few institutions in the world at which a large amount of work
has been done in this line is the private observatory of Dr. C. Dorno,
at Davos, the well-known health resort in the Alps. Dorno’s studies
throw a good deal of light upon the therapeutic effects of sunshine in
a mountain climate.

Many forms of dust in the atmosphere are capable of producing
pronounced physiological and pathological effects. There is a long
list of “dusty trades” in which the production of excessive dust has
notoriously evil effects upon the health of workmen, leading especially
to pulmonary diseases; sometimes to various kinds of poisoning. These
harmful dusts are by no means confined to factories, mines, quarries,
and the like. The air of the average city street abounds in them. Dr.
J. G. Ogden states that 61 per cent of the dust found in the air of the
New York subways consists of jagged splinters of steel, resulting from
the wearing away of brake shoes, wheels, and rails.

The amount of danger to human health incurred through the presence
of disease germs in the atmosphere has been the subject of much
controversy. The present tendency is to regard this danger as very
slight, under ordinary conditions. Thus, Dr. F. S. Lee writes:

“Evidence that disease germs pass through the air from room to room
of a house or from a hospital to its immediate surroundings always
breaks down when examined critically. It is indeed not rare now to
treat cases of different infectious diseases in the same hospital
ward. The one place of possible danger is in the immediate vicinity
of a person suffering from a disease affecting the air passages, the
mouth, throat, or lungs, such as a ‘cold’ or tuberculosis. Such a
person may give out the characteristic microbe for a distance of a few
feet from his body, not in quiet expiration, for simple expired air is
sterile, but attached to droplets that may be expelled in coughing,
sneezing, or forcible speaking. In this manner infection may, and
probably does, occur, the evidence being perhaps strongest in the case
of tuberculosis. But apart from this source there appears to be little
danger of contracting an infectious disease from germs that float in
the air.”

In regard to sewer gas, which still inspires so much dread in the
popular mind, Dr. Lee says:

“Workmen in sewers are notoriously strong, vigorous, healthy men,
with a low death rate among them. The specter of an invisible monster
entering our homes surreptitiously from our plumbing pipes and sapping
our lives and the lives of our children must be laid aside; we need no
longer leave saucers of so-called ‘chlorides’ standing about our floors
to neutralize in an impossible manner mysterious effluvia that do not
exist; and when we return to our town houses in the autumn we may enter
them with no fears that we are risking our lives by coming into a
toxic, germ-infected, sewer gas-laden, deadly atmosphere.”

Present-day knowledge on the subject of infectious diseases discredits
many ideas that once prevailed with regard to the effects of tropical
climates on health. The remarkable results accomplished by vigorous
sanitary measures in such places as Havana, the Isthmus of Panama and
Guayaquil have aroused hopes--perhaps too sanguine--that eventually
all parts of the tropics will be made healthful for the white race. In
the Canal Zone the death rate of the large population of American men,
women, and children is not higher than prevails in many cities of the
United States; whereas, a generation ago, when the French were at work
on the canal, the “climate” of this region was regarded as one of the
most unhealthful in the world. Some authorities go so far as to assert
that the deterioration in the general health and efficiency of white
people in the tropics, so far as it actually occurs, is due entirely
to preventable diseases. It would seem more rational, however, to
assume that there are climates both in and out of the tropics which,
on account of their heat, humidity, and other purely physical factors,
are not so suitable for habitation for any race of humanity as others.
How far acclimatization can go toward offsetting the effects of these
atmospheric conditions is problematical.

The changes in the barometer that occur from day to day in regions
where these changes are most pronounced are, on an average,
not greater than those encountered in going from the bottom to
the top of a good-sized hill, and are probably not directly of
physiological importance. Certain European investigators, however,
ascribe pathological effects to the minute and rapid barometric
fluctuations--too small to be detected with an ordinary barometer--that