Skate on ice (J. Müller) - - - 0.016--0.032
Best-greased surfaces (Perry) - 0.03--0.036

You perceive from the table that while the friction of brass or
aluminium on glass is quite independent of the weight used, that
of brass or aluminium on ice depends in some way upon the weight,
and falls in a very marked degree when the weight is heavy. Now,
I think that if we had been on the look out for any abnormality
in the friction of hard substances on ice, we would have rather
anticipated a variation in the

265

other direction. We would have, perhaps, expected that a heavy
weight would have given rise to the greater friction. I now turn
to the explanation of this extraordinary result.

You are aware that it requires an expenditure of heat merely to
convert ice to water, the water produced being at the temperature
of the ice, _i.e._ at 0° C., from which it is derived. The heat
required to change the ice from the solid to the liquid state is
the latent heat of water. We take the unit quantity of heat to be
that which is required to heat 1 kilogram of water 1° C. Then if
we melt 1 kilogram of ice, we must supply it with 80 such units
of heat. While melting is going on, there is no change of
temperature if the experiment is carefully conducted. The melting
ice and the water coming from it remain at 0° C. throughout the
operation, and neither the thermometer nor your own sensations
would tell you of the amount of heat which was flowing in. The
heat is latent or hidden in the liquid produced, and has gone to
do molecular work in the substance. Observe that if we supply
only 40 thermal units, we get only one-half the ice melted. If
only 10 units are supplied, then we get only one eighth of a
kilogram of water, and no more nor less.

I have ventured to recall to you these commonplaces of science
before considering a mode of melting ice which is less generally
known, and which involves no supply of heat on your part. This
method involves for its

266

understanding a careful consideration of the thermal properties
of water in the solid state.

It must have been observed a very long time ago that water
expands when it freezes. Otherwise ice would not float on water;
and, what is perhaps more important in your eyes, your water
pipes would not burst in winter when the water freezes therein.
But although the important fact of the expansion of water on
freezing was so long presented to the observation of mankind, it
was not till almost exactly the middle of the last century that
James Thomson, a gifted Irishman, predicted many important
consequences arising from the fact of the expansion of water on
becoming solid. The principles lie enunciated are perfectly
general, and apply in every case of change of volume attending
change of state. We are here only concerned with the case of
water and ice.

James Thomson, following a train of thought which we cannot here
pursue, predicted that owing to the fact of the expansion of
water on becoming solid, pressure will lower the melting point of
ice or the freezing point of water. Normally, as you are aware,
the temperature is 0° C. or 32° F. Thomson said that this would
be found to be the freezing point only at atmospheric pressure.
He calculated how much it would change with change of pressure.
He predicted that the freezing point would fall 0.0075 of a
degree Centigrade for each additional atmosphere of pressure
applied to the water. Suppose,

267

for instance, our earth possessed an atmosphere so heavy to as
exert a thousand times the pressure of the existing atmosphere,
then water would not freeze at 0° C., but at -7.5° C. or about
18° F. Again, in vacuo, that is when the pressure has been
reduced to the relatively small vapour pressure of the water, the
freezing point is above 0° C., _i.e._ at 0.0075° C. In parts of
the ocean depths the pressure is much over a thousand
atmospheres. Fresh water would remain liquid there at
temperatures much below 0° C.

It will be evident enough, even to those not possessed of the
scientific insight of James Thomson, that some such fact is to be
anticipated. It is, however, easy to be wise after the event. It
appeals to us in a general way that as water expands on freezing,
pressure will tend to resist the turning of it to ice. The water
will try to remain liquid in obedience to the pressure. It will,
therefore, require a lower temperature to induce it to become
ice.

James Thomson left his thesis as a prediction. But he predicted
exactly what his distinguished brother, Sir William Thomson--later
Lord Kelvin--found to happen when the matter was put to the test
of experiment. We must consider the experiment made by Lord
Kelvin.

According to Thomson's views, if a quantity of ice and water are
compressed, there must be _a fall of temperature_. The nature of
his argument is as follows:

268

Let the ice and water be exactly at 0° C. to start with. Then
suppose we apply, say, one thousand atmospheres pressure. The
melting point of the ice is lowered to -7.5° C. That is, it will
require a temperature so low as -7.5° C. to keep it solid. It
will therefore at once set about melting, for as we have seen,
its actual temperature is not -7.5° C., but a higher temperature,
_i.e._ 0° C. In other words, it is 7.5° above its melting point.
But as soon as it begins melting it also begins to absorb heat to
supply the 80 thermal units which, as we know, are required to
turn each kilogram of the ice to water. Where can it get this
heat? We assume that we give it none. It has only two sources,
the ice can take heat from itself, and it can take heat from the
water. It does both in this case, and both ice and water drop in
temperature. They fall in temperature till -7.5° is reached. Then
the ice has got to its melting point under the pressure of one
thousand atmospheres, or, as we may put it, the water has reached
its freezing point. There can be no more melting. The whole mass
is down to -7.5° C., and will stay there if we keep heat from
flowing either into or out of the vessel. There is now more water
and less ice in the vessel than when we started, and the
temperature has fallen to -7.5° C. The fall of temperature to the
amount predicted by the theory was verified by Lord Kelvin.

Suppose we now suddenly remove the pressure; what will happen? We
have water and ice at -7.5° C.

269

and at the normal pressure. Water at -7.5° and at the normal
pressure of course turns to ice. The water will, therefore,
instantly freeze in the vessel, and the whole process will be
reversed. In freezing, the water will give up its latent heat,
and this will warm up the whole mass till once again 0° C. is
attained. Then there will be no more freezing, for again the ice
is at its melting point. This is the remarkable series of events
which James Thomson predicted. And these are the events which
Lord Kelvin by a delicate series of experiments, verified in
every respect.

Suppose we had nothing but solid ice in the vessel at starting,
would the experiment result in the same way? Yes, it assuredly
would. The ice under the increased pressure would melt a little
everywhere throughout its mass, taking the requisite latent heat
from itself at the expense of its sensible heat, and the
temperature of the ice would fall to the new melting point.

Could we melt the whole of the ice in this manner? Again the
answer is "yes." But the pressure must be very great. If we
assume that all the heat is obtained at the expense of the
sensible heat of the ice, the cooling must be such as to supply
the latent heat of the whole mass of water produced. However, the
latent heat diminishes as the melting point is lowered, and at a
rate which would reduce it to nothing at about 18,000
atmospheres. Mousson, operating on ice enclosed in a conducting
cylinder and cooled to -18° at starting

270

appears to have obtained very complete liquefaction. Mousson must
have attained a pressure of at least an amount adequate to lower
the melting point below -18°. The degree of liquefaction actually
attained may have been due in part to the passage of heat through
the walls of the vessel. He proved the more or less complete
liquefaction of the ice within the vessel by the fall of a copper
index from the top to the bottom of the vessel while the pressure
was on.

I have here a simple way of demonstrating to you the fall of
temperature attending the compression of ice. In this mould,
which is strongly made of steel, lined with boxwood to diminish
the passage of conducted heat, is a quantity of ice which I
compress when I force in this plunger. In the ice is a
thermoelectric junction, the wires leading to which are in
communication with a reflecting galvanometer. The thermocouple is
of copper and nickel, and is of such sensitiveness as to show by
motion of the spot of light on the screen even a small fraction
of a degree. On applying the pressure, you see the spot of light
is displaced, and in such a direction as to indicate cooling. The
balancing thermocouple is all the time imbedded in a block of ice
so that its temperature remains unaltered. On taking off the
pressure, the spot of light returns to its first position. I can
move the spot of light backwards and forwards on the screen by
taking off and putting on the pressure. The effects are quite
instantaneous.

271

The fact last referred to is very important. The ice, in fact, is
as it were automatically turned to water. It is not a matter of
the conduction of heat from point to point in the ice. Its own
sensible heat is immediately absorbed throughout the mass. This
would be the theoretical result, but it is probable that owing to
imperfections throughout the ice and failure in uniformity in the
distribution of the stress, the melting would not take place
quite uniformly or homogeneously.

Before applying our new ideas to skating, I want you to notice a
fact which I have inferentially stated, but not specifically
mentioned. Pressure will only lead to the melting of ice if the
new melting point, _i.e._ that due to the pressure, is below the
prevailing temperature. Let us take figures. The ice to start
with is, say, at -3° C. Suppose we apply such a pressure to this
ice as will confer a melting point of -2° C. on it. Obviously,
there will be no melting. For why should ice which is at -3° C.
melt when its melting point is -2° C.? The ice is, in fact,
colder than its melting point. Hence, you note this fact: The
pressure must be sufficiently intense to bring the melting point
below the prevailing temperature, or there will be no melting;
and the further we reduce the melting point by pressure below the
prevailing temperature, the more ice will be melted.

We come at length to the object of our remarks I don't know who
invented skating or skates. It is said that in the thirteenth
century the inhabitants of

272

England used to amuse themselves by fastening the bones of an
animal beneath their feet, and pushing themselves about on the
ice by means of a stick pointed with iron. With such skates, any
performance either on inside or outside edge was impossible. We
are a conservative people. This exhilarating amusement appears to
have served the people of England for three centuries. Not till
1660 were wooden skates shod with iron introduced from the
Netherlands. It is certain that skating was a fashionable
amusement in Pepys' time. He writes in 1662 to the effect: "It
being a great frost, did see people sliding with their skates,
which is a very pretty art." It is remarkable that it was the
German poet Klopstock who made skating fashionable in Germany.
Until his time, the art was considered a pastime, only fit for
very young or silly people.

I wish now to dwell upon that beautiful contrivance the modern
skate. It is a remarkable example of how an appliance can develop
towards perfection in the absence of a really intelligent
understanding of the principles underlying its development. For
what are the principles underlying the proper construction of the
skate? After what I have said, I think you will readily
understand. The object is to produce such a pressure under the
blade that the ice will melt. We wish to establish such a
pressure under the skate that even on a day when the ice is below
zero, its melting

273

point is so reduced just under the edge of the skate that the ice
turns to water.

It is this melting of the ice under the skate which secures the
condition essential to skating. In the first place, the skate no
longer rests on a solid. It rests on a liquid. You are aware how
in cases where we want to reduce friction--say at the bearing of a
wheel or under a pivot--we introduce a liquid. Look at the
bearings of a steam engine. A continuous stream of oil is fed in
to interpose itself between the solid surfaces. I need not
illustrate so well-known a principle by experiment. Solid
friction disappears when the liquid intervenes. In its place we
substitute the lesser difficulty of shearing one layer of the
liquid over the other; and if we keep up the supply of oil the
work required to do this is not very different, no matter how
great we make the pressure upon the bearings. Compared with the
resistance of solid friction, the resistance of fluid friction is
trifling. Here under the skate the lubrication is perhaps the
most perfect which it is possible to conceive. J. Müller has
determined the coefficient by towing a skater holding on by a
spring balance. The coefficient is between 0.016 and 0.032. In
other words, the skater would run down an incline so little as 1
or 2 degrees; an inclination not perceivable by the eye. Now
observe that the larger of these coefficients is almost exactly
the same as that which Perry found in the case of well-greased
surfaces. But evidently no

274

artificial system of lubrication could hope to equal that which
exists between the skate and the ice. For the lubrication here
is, as it were, automatic. In the machine if the lubricant gets
squeezed out there instantly ensues solid friction. Under the
skate this cannot happen for the squeezing out of the lubricant
is instantly followed by the formation of another film of water.
The conditions of pressure which may lead to solid friction in
the machine here automatically call the lubricant into
existence.

Just under the edge of the skate the pressure is enormous.
Consider that the whole weight of the skater is born upon a mere
knife edge. The skater alternately throws his whole weight upon
the edge of each skate. But not only is the weight thus
concentrated upon one edge, further concentration is secured in
the best skates by making the skate hollow-ground, _i.e._
increasing the keenness of the edge by making it less than a
right angle. Still greater pressure is obtained by diminishing
the length of that part of the blade which is in contact with the
ice. This is done by putting curvature on the blade or making it
what is called "hog-backed." You see that everything is done to
diminish the area in contact with the ice, and thus to increase
the pressure. The result is a very great compression of the ice
beneath the edge of the skate. Even in the very coldest weather
melting must take place to some extent.

As we observed before, the melting is instantaneous,

275

Heat has not to travel from one point of the ice to another;
immediately the pressure comes on the ice it turns to water. It
takes the requisite heat from itself in order that the change of
state may be accomplished. So soon as the skate passes on, the
water resumes the solid state. It is probable that there is an
instantaneous escape, and re-freezing of some of the water from
beneath the skate, the skate instantly taking a fresh bearing and
melting more ice. The temperature of the water escaping from
beneath the skate, or left behind by it, immediately becomes what
it was before the skate pressed upon it.

Thus, a most wonderful and complex series of molecular events
takes place beneath the skate. Swift as it passes, the whole
sequence of events which James Thomson predicted has to take
place beneath the blade Compression; lowering of the melting
point below the temperature of the surrounding ice; melting;
absorption of heat; and cooling to the new melting point, _i.e._
to that proper to the pressure beneath the blade. The skate now
passes on. Then follow: Relief of pressure; re-solidification of
the water; restoration of the borrowed heat from the congealing
water and reversion of the ice to the original temperature.

If we reflect for a moment on all this, we see that we do not
skate on ice but on water. We could not skate on ice any more
than we could skate on glass. We saw that with light weights and
when the pressure

276

{Diagram}

Diagram showing successive states obtaining in ice, before,
during, and after the passage of the skate. The temperatures and
pressures selected for illustration are such as might occur under
ordinary conditions. The edge of the skate is shown in magnified
cross-section.

277

Was not sufficient to melt the ice, the friction was much the
same as that of metal on glass. Ice is not slippery. It is an
error to say that it is. The learned professor was very much
astray when he said that you could skate on ice because it is so
smooth. The smoothness of the ice has nothing to do with the
matter. In short, owing to the action of gravity upon your body,
you escape the normal resistance of solid on solid, and glide
about with feet winged like the messenger of the Gods; but on
water.

A second condition essential to the art of skating is also
involved in the melting of the ice. The sinking of the skate
gives the skater "bite." This it is which enables him to urge
himself forward. So long as skates consisted of the rounded bones
of animals, the skater had to use a pointed staff to propel
himself. In creating bite, the skater again unconsciously appeals
to the peculiar physical properties of ice. The pressure required
for the propulsion of the skater is spread all along the length
of the groove he has cut in the ice, and obliquely downwards. The
skate will not slip away laterally, for the horizontal component
of the pressure is not enough to melt the ice. He thus gets the
resistance he requires.

You see what a very perfect contrivance the skate is; and what a
similitude of intelligence there is in its evolution. Blind
intelligence, because it is certain the true physics of skating
was never held in view by

278

the makers of skates. The evolution of the skate has been truly
organic. The skater selected the fittest skate, and hence the fit
skate survived.

In a word, the possibility of skating depends on the dynamical
melting of ice under pressure. And observe the whole matter turns
upon the apparently unrelated fact that the freezing of water
results in a solid more bulky than the water which gives rise to
it. If ice was less bulky than the water from which it was
derived, pressure would not melt it; it would be all the more
solid for the pressure, as it were. The melting point would rise
instead of falling. Most substances behave in this manner, and
hence we cannot skate upon them. Only quite a few substances
expand on freezing, and it happens that their particular melting
temperatures or other properties render them unsuitable to
skating. The most abundant fluid substance on the earth, and the
most abundant substance of any one kind on its surface, thus
possesses the ideally correct and suitable properties for the art
of skating.

I have pointed out that the pressure must be such as to bring the
temperature of melting below that prevailing in the ice at the
time. We have seen also, that one atmosphere lowers the melting
point of ice by the 1/140 of a degree Centigrade; more exactly by
0.0075°. Let us now assume that the skate is so far sunken in the
ice as to bear for a length of two inches, and for a width of
one-hundredth of an inch. The skater weighs,

279

let us say--150 pounds. If this weight was borne on one square
inch, the pressure would be ten atmospheres. But the skater rests
his weight, in fact, upon an area of one-fiftieth of an inch. The
pressure is, therefore, fifty times as great. The ice is
subjected to a pressure of 500 atmospheres. This lowers the
melting point to -3.75° C. Hence, on a day when the ice is at
this temperature, the skate will sink in the ice till the weight
of the skater is concentrated as we have assumed. His skate can
sink no further, for any lesser concentration of the pressure
will not bring the melting point below the prevailing
temperature. We can calculate the theoretical bite for any state
of the ice. If the ice is colder the bite will not be so deep. If
the temperature was twice as far below zero, then the area over
which the skater's weight will be distributed, when the skate has
penetrated its maximum depth, will be only half the former area,
and the pressure will be one thousand atmospheres.

An important consideration arises from the fact that under the
very extreme edge of the skate the pressure is indefinitely
great. For this involves that there will always be some bite,
however cold the ice may be. That is, the narrow strip of ice
which first receives the skater's weight must partially liquefy
however cold the ice.

It must have happened to many here to be on ice which was too
cold to skate on with comfort. The

280

skater in this case speaks of the ice as too hard. In the
Engadine, the ice on the large lakes gets so cold that skaters
complain of this. On the rinks, which are chiefly used there, the
ice is frequently renewed by flooding with water at the close of
the day. It thus never gets so very cold as on the lakes. I have
been on ice in North France, which, in the early morning, was too
hard to afford sufficient bite for comfort. The cause of this is
easily understood from what we have been considering.

We may now return to the experimental results which we obtained
early in the lecture. The heavy weights slip off the ice at a low
angle because just at the points of contact with the ice the
latter melts, and they, in fact, slip not on ice but on water.
The light weights on cold, dry ice do not lower the melting point
below the temperature of the ice, _i.e._ below -10° C., and so
they slip on dry ice. They therefore give us the true coefficient
of friction of metal on ice.

This subject has, more recently been investigated by H. Morphy,
of Trinity College, Dublin. The refinement of a closed vessel at
uniform temperature, in which the ice is formed and the
experiment carried out, is introduced. Thermocouples give the
temperatures, not only of the ice but of the aluminium sleigh
which slips upon it under various loads. In this way we may be
certain that the metal runners are truly at the temperature of
the ice. I now quote from Morphy's paper

281

"The angle of friction was found to remain constant until a
certain stage of the loading, when it suddenly fell to about half
of its original value. It then remained constant for further
increases in the load.

"These results, which confirmed those obtained previously with
less satisfactory apparatus, are shown in the table below. In the
first column is shown the load, _i.e._ the weight of sleigh +
weight of shot added. In the second and third columns are shown,
respectively, the coefficient and angle of friction, whilst the
fourth gives the temperature of the ice as determined from the
galvanometer deflexions.

Load.        Tan y.          y.        Temp.

5.68 grams.  0.36±.01     20°±30'    -5.65° C.
10.39                                -5.65°
11.96                                -5.75°
12.74                                -5.60°
13.53                                -5.65°
14.31                                -5.65°
15.10 grams. 0.17±.01    9°.30'±30'  -5.60°
16.67                                -5.55°
19.81                                -5.60°
24.52                                -5.60°
5.68 grams. 0.36±.01      20°±30'    -5.60°

"These experiments were repeated on another occasion with the same
result and similar results had been obtained with different
apparatus.

"As a result of the investigation the following points are
clearly shown:--

282

"(1) The coefficient of friction for ice at constant temperature
may have either of two constant values according to the pressure
per unit surface of contact.

"(2) For small pressures, and up to a certain well defined limit
of pressure, the coefficient is fairly large, having the value
0.36±.01 in the case investigated.

"(3) For pressures greater than the above limit the coefficient
is relatively small, having the value 0.17±.01 in the case
investigated."

It will be seen that Morphy's results are similar to those
arrived at in the first experimental consideration of our
subject; but from the manner in which the experiments have been
carried out, they are more accurate and reliable.

A great deal more might be said about skating, and the allied
sports of tobogganing, sleighing, curling, ice yachting, and
last, but by no means least, sliding--that unpretentious pastime
of the million. Happy the boy who has nails in his boots when
Jack-Frost appears in his white garment, and congeals the
neighbouring pond. But I must turn away at the threshold of the
humorous aspect of my subject (for the victim of the street
"slide" owes his injured dignity to the abstruse laws we have
been discussing) and pass to other and graver subjects intimately
connected with skating.

James Thomson pointed out that if we apply compressional stress
to an ice crystal contained in a vessel

283

which also contains other ice crystals, and water at 0° C., then
the stressed crystal will melt and become water, but its
counterpart or equivalent quantity of ice will reappear elsewhere
in the vessel. This is, obviously, but a deduction from the
principles we have been examining. The phenomenon is commonly
called "regelation." I have already made the usual regelation
experiment before you when I compressed broken ice in this mould.
The result was a clear, hard and almost flawless lens of ice. Now
in this operation we must figure to ourselves the pieces of ice
when pressed against one another melting away where compressed,
and the water produced escaping into the spaces between the
fragments, and there solidifying in virtue of its temperature
being below the freezing point of unstressed water. The final
result is the uniform lens of ice. The same process goes on in a
less perfect manner when you make--or shall I better say--when you
made snowballs.

We now come to theories of glacier motion; of which there are
two. The one refers it mainly to regelation; the other to a real
viscosity of the ice.

The late J. C. M'Connel established the fact that ice possesses
viscosity; that is, it will slowly yield and change its shape
under long continued stresses. His observations, indeed, raise a
difficulty in applying this viscosity to explain glacier motion,
for he showed that an ice crystal is only viscous in a certain
structural

284

direction. A complex mixture of crystals such, as we know glacier
ice to be, ought, we would imagine, to display a nett or
resultant rigidity. A mass of glacier ice when distorted by
application of a force must, however, undergo precisely the
transformations which took place in forming the lens from the
fragments of ice. In fact, regelation will confer upon it all the
appearance of viscosity.

Let us picture to ourselves a glacier pressing its enormous mass
down a Swiss valley. At any point suppose it to be hindered in
its downward path by a rocky obstacle. At that point the ice
turns to water just as it does beneath the skate. The cold water
escapes and solidifies elsewhere. But note this, only where there
is freedom from pressure. In escaping, it carries away its latent
heat of liquefaction, and this we must assume, is lost to the
region of ice lately under pressure. This region will, however,
again warm up by conduction of heat from the surrounding ice, or
by the circulation of water from the suxface. Meanwhile, the
pressure at that point has been relieved. The mechanical
resistance is transferred elsewhere. At this new point there is
again melting and relief of pressure. In this manner the glacier
may be supposed to move down. There is continual flux of
conducted heat and converted latent heat, hither and thither, to
and from the points of resistance. The final motion of the whole
mass is necessarily slow; a few feet in the day or, in winter,

285

even only a few inches. And as we might expect, perfect silence
attends the downward slipping of the gigantic mass. The motion
is, I believe, sufficiently explained as a skating motion. The
skate is, however, fixed, the ice moves. The great Aletsch
Glacier collects its snows among the highest summits of the
Oberland. Thence, the consolidated ice makes its way into the
Rhone Valley, travelling a distance of some 20 miles. The ice now
melting into the youthful Rhone fell upon the Monch, the Jungfrau
or the Eiger in the days when Elizabeth ruled in England and
Shakespeare lived.

The ice-fall is a common sight on the glacier. In great lumps and
broken pinnacles it topples over some rocky obstacle and falls
shattered on to the glacier below. But a little further down the
wound is healed again, and regelation has restored the smooth
surface of the glacier. All such phenomena are explained on James
Thomson's exposition of the behaviour of a substance which
expands on passing from the liquid to the solid state.

We thus have arrived at very far-reaching considerations arising
out of skating and its science. The tendency for snow to
accumulate on the highest regions of the Earth depends on
principles which we cannot stop to consider. We know it collects
above a certain level even at the Equator. We may consider, then,
that but for the operation of the laws which James Thomson
brought to light, and which his illustrious brother,

286

Lord Kelvin, made manifest, the uplands of the Earth could not
have freed themselves of the burthen of ice. The geological
history of the Earth must have been profoundly modified. The
higher levels must have been depressed; the general level of the
ocean relatively to the land thereby raised, and, it is even
possible, that such a mean level might have been attained as
would result in general submergence.

During the last great glacial period, we may say the fate of the
world hung on the operation of those laws which have concerned us
throughout this lecture. It is believed the ice was piled up to a
height of some 6,000 feet over the region of Scandinavia. Under
the influence of the pressure and fusion at points of resistance,
the accumulation was stayed, and it flowed southwards the
accumulation was stayed, and it flowed southwards over Northern
Europe. The Highlands of Scotland were covered with, perhaps,
three or four thousand feet of ice. Ireland was covered from
north to south, and mighty ice-bergs floated from our western and
southern shores.

The transported or erratic stones, often of great size, which are
found in many parts of Ireland, are records of these long past
events: events which happened before Man, as a rational being,
appeared upon the Earth.

287

A SPECULATION AS TO A PREMATERIAL UNIVERSE [1]

"And therefore...these things likewise had a birth; for things
which are of mortal body could not for an infinite time back...
have been able to set at naught the puissant strength of
immeasurable age."--LUCRETIUS, _De Rerum Natura._

"O fearful meditation! Where, alack! Shall Time's best jewel
from Time's chest lie hid?" --SHAKESPEARE.

IN the material universe we find presented to our senses a
physical development continually progressing, extending to all,
even the most minute, material configurations. Some fundamental
distinctions existing between this development as apparent in the
organic and the inorganic systems of the present day are referred
to elsewhere in this volume.[2] In the present essay, these
systems as having a common origin and common ending, are merged
in the same consideration as to the nature of the origin of
material systems in general. This present essay is occupied by
the consideration of the necessity of limiting material
interactions in past time. The speculation originated in the
difficulties which present themselves when we ascribe to these
interactions infinite duration in the past. These difficulties
first claim our consideration.

[1] Proc. Royal Dublin Soc., vol. vii., Part V, 1892.

[2] _The Abundance of Life._

288

Accepting the hypothesis of Kant and Laplace in its widest
extension, we are referred to a primitive condition of wide
material diffusion, and necessarily too of material instability.
The hypothesis is, in fact, based upon this material instability.
We may pursue the sequence of events assumed in this hypothesis
into the future, and into the past.

In the future we find finality to progress clearly indicated. The
hypothesis points to a time when there will be no more
progressive change but a mere sequence of unfruitful events, such
as the eternal uniform motion of a mass of matter no longer
gaining or losing heat in an ether possessed of a uniform
distribution of energy in all its parts. Or, again, if the ether
absorb the energy of material motion, this vast and dark
aggregation eternally poised and at rest within it. The action is
transferred to the subtle parts of the ether which suffer none of
the energy to degrade. This is, physically, a thinkable future.
Our minds suggest no change, and demand none. More than this,
change is unthinkable according to our present ideas of energy.
Of progress there is an end.

This finality _â parte post_ is instructive. Abstract
considerations, based on geometrical or analytical illustrations,
question the finiteness of some physical developments. Thus our
sun may require eternal time to attain the temperature of the
ether around it, the approach to this condition being assumed to
be asymptotic in

289

character. But consider the legitimate _reductio ad absurdum_ of
an ember raked from a fire 1000 years ago. Is it not yet cooled
down to the constant temperature of its surroundings? And we may
evidently increase the time a million-fold if we please. It
appears as if we must regard eternity as outliving every
progressive change, For there is no convergence or enfeeblement
of time. The ever-flowing present moves no differently for the
occurrence of the mightiest or the most insignificant events. And
even if we say that time is only the attendant upon events, yet
this attendant waits patiently for the end, however long
deferred.

Does the essentially material hypothesis of Kant and Laplace
account for an infinite past as thinkably as it accounts for the
infinite future? As this hypothesis is based upon material
instability the question resolves itself into this:-- Is the
assumption of an infinitely prolonged past instability a probable
or possible account of the past? There are, it appears to me,
great difficulties involved in accepting the hypothesis of
infinitely prolonged material instability. I will refer here to
three principal objections. The first may be called a
metaphysical objection; the second is partly metaphysical and
partly physical, the third may be considered a physical
objection, as it is involved directly in the phenomena presented
by our universe.

The metaphysical objection must have presented itself to every
one who has considered the question. It may

290

be put thus:--If present events are merely one stage in an
infinite progress, why is not the present stage long ago passed
over? We are evidently at liberty to push back any stage of
progress to as remote a period as we like by putting back first
the one before this and next the stage preceding this, and so on,
for, by hypothesis, there is no beginning to the progress.

Thus, the sum of passing events constituting the present universe
should long ago have been accomplished and passed away. If we
consider alternative hypotheses not involving this difficulty, we
are at once struck by the fact that the future of material
development is free of the objection. For the eternity of
unprogressive events involved in the future on Kant's hypothesis,
is not only thinkable, but any change is, as observed,
irreconcilable with our ideas of energy. As in the future so in
the past we look to a cessation to progress. But as we believe
the activity of the present universe must in some form have
existed all along, the only refuge in the past is to imagine an
active but unprogressive eternity, the unprogressive activity at
some period becoming a progressive activity--that progressive
activity of which we are spectators. To the unprogressive
activity there was no beginning; in fact, beginning is as
unthinkable and uncalled for to the unprogressive activity of the
past as ending is to the unprogressive activity of the future,
when all developmental actions shall have ceased. There is no
beginning or ending to the activity of the universe.

291

There is beginning and ending to present progressive activity.
Looking through the realm of nature we seek beginning and ending,
but "passing through nature to eternity" we find neither. Both
are justified; the questioning of the ancient poet regarding the
past, and of the modern regarding the future, quoted at the head
of this essay.

The next objection, which is in part metaphysical, is founded on
the difficulty of ascribing any ultimate reality or potency to
forces diminishing through eternal time. Thus, against the
assumption that our universe is the result of material
aggregation progressing over eternal time, which involves the
primitive infinite separation of the particles, we may ask, what
force can have acted between particles sundered by infinite
distance? The gravitational force falling off as the square of
the distance, must vanish at infinity if we mean what we say when
we ascribe infinite separation to them. Their condition is then
one of neutral stability, a finite movement of the particles
neither increasing nor diminishing interaction. They had then
remained eternally in their separated condition, there being no
cause to render such condition finite. The difficulty involved
here appears to me of the same nature as the difficulty of
ascribing any residual heat to the sun after eternal time has
elapsed. In both cases we are bound to prolong the time, from our
very idea of time, till progress is no more, when in the one case
we can imagine no mutual approximation of the

292

particles, in the other no further cooling of the body. However,
I will riot dwell further upon this objection, as it does not, I
believe, present itself with equal force to every mind. A reason
less open to dispute, as being less subjective, against the
aggregation of infinitely remote particles as the origin of our
universe, is contained in the physical objection.

In this objection we consider that the appearance presented by
our universe negatives the hypothesis of infinitely prolonged
aggregation. We base this negation upon the appearance of
simultaneity ~ presented by the heavens, contending that this
simultaneity is contrary to what we would expect to find in the
case of particles gathered from infinitely remote distances.
Whether these particles were endowed with relative motions or not
is unimportant to the consideration. In what respects do the
phenomena of our universe present the appearance of simultaneous
phenomena? We must remember that the suns in space are as fires
which brighten only for a moment and are then extinguished. It is
in this sense we must regard the longest burning of the stars.
Whether just lit or just expiring counts little in eternity. The
light and heat of the star is being absorbed by the ether of
space as effectually and rapidly as the ocean swallows the ripple
from the wings of an expiring insect. Sir William Herschel says
of the galaxy of the milky way:-- "We do not know the rate of
progress of this mysterious chronometer, but it is nevertheless
certain that it cannot

293

last for ever, and its past duration cannot be infinite." We do
not know, indeed, the rate of progress of the chronometer, but if
the dial be one divided into eternal durations the consummation
of any finite physical change represents such a movement of the
hand as is accomplished in a single vibration of the balance
wheel.

Hence we must regard the hosts of glittering stars as a
conflagration that has been simultaneously lighted up in the
heavens. The enormous (to our ideas) thermal energy of the stars
resembles the scintillation of iron dust in a jar of oxygen when
a pinch of the dust is thrown in. Although some particles be
burnt up before others become alight, and some linger yet a
little longer than the others, in our day's work the
scintillation of the iron dust is the work of a single instant,
and so in the long night of eternity the scintillation of the
mightiest suns of space is over in a moment. A little longer,
indeed, in duration than the life which stirs a moment in
response to the diffusion of the energy, but only very little. So
must an Eternal Being regard the scintillation of the stars and
the periodic vibration of life in our geological time and the
most enduring efforts of thought. The latter indeed are no more
lasting than

"... the labour of ants In the light of a million million of
suns."

But the myriad suns themselves, with their generations, are the
momentary gleam of lights for ever after extinguished.

294

Again, science suggests that the present process of material
aggregation is not finished, and possibly will only be when it
prevails universally. Hence the very distribution of the stars,
as we observe them, as isolated aggregations, indicates a
development which in the infinite duration must be regarded as
equally advanced in all parts of stellar space and essentially a
simultaneous phenomenon. For were we spectators of a system in
which any very great difference of age prevailed, this very great
difference would be attended by some such appearance as the
following:--

The aupearance of but one star, other generations being long
extinct or no others yet come into being; or, perhaps, a faint
nebulous wreath of aggregating matter somewhere solitary in the
heavens; or no sign of matter beyond our system, either because
ungathered or long passed away into darkness.[1]

Some such appearances were to be expected had the aggregation of
matter depended solely on chance encounters of particles
scattered through infinite space.

For as, by hypothesis, the aggregation occupies an infinite time
in consummation it is nearly a certainty that each particle
encountered after immeasurable time, and then for the first time
endowed with actual gravitational potential energy, would have
long expended this energy

[1] It is interesting to reflect upon the effect which an entire
absence of luminaries outside our solar system would have had
upon the views of our philosophers and upon our outlook on life.

295

before another particle was gathered. But the fact that so many
fires which we know to be of brief duration are scattered through
a region of space, and the fact of a configuration which we
believe to be a transitory ore, suggest their simultaneous
aggregation here and there. And in the nebulous wreaths situated
amidst the stars there is evidence that these actually originated
where they now are, for in such no relative motion, I believe,
has as yet been detected by the spectroscope. All this, too, is
in keeping with the nebular hypothesis of Kant and Laplace so
long as this does not assume a primitive infinite dispersion of
matter, but the gathering of matter from finite distances first
into nebulous patches which aggregating with each other have
given rise to our system of stars. But if we extend this
hypothesis throughout an infinite past by the supposition of
aggregation of infinitely remote particles we replace the
simultaneous approach required in order to accotnt for the
simultaneous phenomena visible in the heavens, by a succession of
aggregative events, by hypothesis at intervals of nearly infinite
duration, when the events of the universe had consisted of fitful
gleams lighted after eternities of time and extinguished for yet
other eternities.

Finally, if we seek to replace the eternal instability involved
in Kant's hypothesis when extended over an infinite past, by any
hypothesis of material stability, we at once find ourselves in
the difficulty that from the known properties of matter such
stability must have been

296

permanent if ever existent, which is contrary to fact. Thus the
kinetic inertia expressed in Newton's first law of motion might
well be supposed to secure equilibrium with material attraction,
but if primevally diffused matter had ever thus been held in
equilibrium it must have remained so, or it was maintained so
imperfectly, which brings us back to endless evolution.

On these grounds I contend that the present gravitational
properties of matter cannot be supposed to have acted for all
past duration. Universal equilibrium of gravitating particles
would have been indestructible by internal causes. Perpetual
instability or evolution is alike unthinkable and contrary to the
phenomena of the universe of which we are cognisant. We therefore
turn from gravitating matter as affording no rational account of
the past. We do so of necessity, however much we feel our
ignorance of the nature of the unknown actions to which we have
recourse.

A prematerial condition of the universe was, we assume, a
condition in which uniformity as regards the average distribution
of energy in space prevailed, but neterogeneity and instability
were possible. The realization of that possibility was the
beginning we seek, and we today are witnesses of the train of
events involved in the breakdown of an eternal past equilibrium.
We are witnesses on this hypothesis, of a catastrophe possibly
confined to certain regions of space, but which is, to the
motions and configurations concerned, absolutely unique,
reversible to

297

its former condition of potential by no process of which we can
have any conception.

Our speculation is that we, as spectators of evolution, are
witnessing the interaction of forces which have not always been
acting. A prematerial state of the universe was one of unfruitful
motions, that is, motions unattended by progressing changes, in
our region of the ether. How extended we cannot say; the nature
of the motions we know not; but the kinetic entities differed
from matter in the one important particular of not possessing
gravitational attraction. Such kinetic configurations we cannot
consider to be matter. It was _possible_ to construct matter by
their summation or linkage as the configuration of the crystal is
possible in the clear supersaturated liquid.

Duration in an ether filled with such motions would pass in a
succession of mere unfruitful events; as duration, we may
imagine, even now passes in parts of the ether similar to our
own. An endless (it may be) succession of unprogressive,
fruitless events. But at one moment in the infinite duration the
requisite configuration of the elementary motions is attained;
solely by the one chance disposition the stability of all must
go, spreading from the fateful point.

Possibly the material segregation was confined to one part of
space, the elementary motions condensing upon transformation, and
so impoverishing the ether around till the action ceased. Again
in the same sense as the

298

stars are simultaneous, so also they may be regarded as uniform
in size, for the difference in magnitude might have been anything
we please to imagine, if at the same time we ascribe sufficient
distance sundering great and small. So, too;, will a dilute
solution of acetate of soda build a crystal at one point, and the
impoverishment of the medium checking the growth in this region,
another centre will begin at the furthest extremities of the
first crystal till the liquid is filled with loose feathery
aggregations comparable in size with one another. In a similar
way the crystallizing out of matter may have given rise, not to a
uniform nebula in space, but to detached nebula, approximately of
equal mass, from which ultimately were formed the stars.

That an all-knowing Being might have foretold the ultimate event
at any preceding period by observing the motions of the parts
then occurring, and reasoning as to the train of consequences
arising from these nations, is supposable. But considerations
arising from this involve no difficulty in ascribing to this
prematerial train of events infinite duration. For progress there
is none, and we can quite as easily conceive of some part of
space where the same Infinite Intelligence, contemplating a
similar train of unfruitful motions, finds that at no time in the
future will the equilibrium be disturbed. But where evolution is
progressing this is no longer conceivable, as being contradictory
to the very idea of progressive development. In this case
Infinite Intelligence

299

_necessarily_ finds, as the result of his contemplation, the
aggregation of matter, and the consequences arising therefrom.

The negation of so primary a material property as gravitation to
these primitive motions of (or in) the ether, probably involves
the negation of many properties we find associated with matter.
Possibly the quality of inertia, equally primary, is involved
with that of gravitation, and we may suppose that these two
properties so intimately associated in determining the motions of
bodies in space were conferred upon the primitive motions as
crystallographic attraction and rigidity are first conferred upon
the solid growing from the supersaturated liquid. But in some
degree less speculative is the supposition that the new order of
motions involved the transformation of much energy into the form
of heat vibrations; so that the newly generated matter, like the
newly formed crystal, began its existence in a medium richly fed
with thermal radiant energy. We may consider that the thermal
conditions were such as would account for a primitive
dissociation of the elements. And, again, we recall how the
physicist finds his estimate of the energy involved in mere
gravitational aggregation inadequate to afford explanation of
past solar heat. It is supposable, on such a hypothesis as we
have been dwelling on, that the entire subsequent gravitational
condensation and conversion of material potential energy, dating
from the first formation of matter to the stage of star
formation

300

may be insignificant in amount compared with the conversion of
etherial energy attending the crystallizing out of matter from
the primitive motions. And thus possibly the conditions then
obtaining involved a progressively increasing complexity of
material structure the genesis of the elements, from an
infra-hydrogen possessing the simplest material configuration,
resulting ultimately in such self-luminous nebula as we yet see
in the heavens.

The late James Croll, in his _Stellar Evolution_, finds objections
to an eternal evolution, one of which is similar to the
"metaphysical" objection urged in this paper. His way out of the
difficulty is in the speculation that our stellar system
originated by the collision of two masses endowed with relative
motion, eternal in past duration, their meeting ushering in the
dawn of evolution. However, the state of aggregation here
assumed, from the known laws of matter and from analogy, calls
for explanation as probably the result of prior diffusion, when,
of course, the difficulty is only put back, not set at rest. Nor
do I think the primitive collision in harmony with the number of
relatively stationary nebula visible in space.

The metaphysical objection is, I find, also urged by George
Salmon, late Provost of Trinity College, in favour of the
creation of the universe.--(_Sermons on Agnosticism_.)

A. Winchell, in _World Life_, says: "We have not

301

the slightest scientific grounds for assuming that matter existed
in a certain condition from all eternity. The essential activity
of the powers ascribed to it forbids the thought; for all that we
know, and, indeed, as the _conclusion_ from all that we know,
primal matter began its progressive changes on the morning of its
existence."

Finally, in reference to the hypothesis of a unique determination
of matter after eternal duration in the past, it may not be out
of place to remind the reader of the complexity which modern
research ascribes to the structure of the atom.

302

INDEX

A.

Abney, Sir Wm., on sensitisers, 210.

Abundance of life, numerical, 98-100.

Adaptation and aggressiveness of the organism, 80.

Additive law, the, with reference to alpha rays, 220.

Age of Earth, comparison of denudative and radioactive methods of
finding, 23-29.

Aletsch glacier, 286.

Allen, Grant, on colour of Alpine plants, 104.

Allen, H. Stanley, on photo-electricity, 203.

Alpha rays, nature of, 214; velocity of, 214; effects of, on
gases, 214; range of, in air, 215; visualised, 218; ionisation
curve of, 216; number of, from one gram of radium, 237; number of
ions made by, 237.

Alpine flowers, intensity of colour of, 102.

Alps, history of, 141; Tertiary denudation of, 148; depth of
sedimentary covering of, 148; evidence of high pressures and
temperatures in, 149; recent theories of formation of, 150 _et
seq._; upheaval of, 147; age of, 147; volcanic phenomena
attending elevation of, 147.

Andes, trough parallel to, 123; not volcanic in origin, 118.

Angle of friction on ice, 261-265, 281-283; on glass, 261-265.

Animate systems, dynamic conditions of, 67; and transfer of
energy, 71; and old age, 72; mechanical imitation of, 76, 77.

Animate and inanimate systems compared, 73-75.

Appalachian range, formation of, 120.

Arrhenius, on elevation of continents, 17.

Aryan Era of India, 136.

Asteroids, probable origin of, 175; discovery of, 175; dimensions
of, 176; orbits of, 176; Mars' moons derived from, 177.

B.

Babbage and Herschel, theory of mountain building, 123.

Babes (and Cornil), size of spores, 98.

Becker, G. F., age of Earth by sodium collection, 14; age of
minerals by lead ratio, 20.

Berthelot, law of maximum work, 62.

Bertrand, Marcel, section of Mont Blanc Massif, 154.

Beta rays, nature of, 246; accompanied by gamma rays, 247;
production of, by gamma rays, 247; as ionising agents, 249.

Biotite, containing haloes, 223; pleochroism of, 235; intensified
pleochroism in halo, 235.

Body and mind, as manifestations of progressiveness of the
organism, 86.

Boltwood, age of minerals by lead ratio, 20.

Bose, theory of latent image, 203.

Bragg and Kleeman, on path of the alpha ray, 215; stopping power,
219; laws affecting ionisation by alpha rays, 220; curve of
ionisation and structure of the halo, 232.

Brecciendecke, sheet of the, 154.

Brdche, sheet of the, 154.

Burrard and Hayden on the Himalaya, 138; sections of the
Himalaya, 139.

C.

Canals and "canali," 166; curvature of, and path of a satellite,
188 _et seq._; double and triple accounted for, 186, 187;
doubling of, 195; disappearance and reappearance of, 196-198;
photography of, 198; not due to cracks, 167; not due to rivers,
167; of Mars, double nature of, 166, 170; crossing dark regions
of planet's surface, 168; of Mars, Lowell's views on, 168 _et
seq._; shown on Lowell's map, investigation of, 192 _et seq._;
radiating, explanation of, 193, 194; number of, 194; developed by
secondary disturbances, 194; nodal development of, due to raised
surface features, 195.

Chamberlin and Salisbury, the Laramide range, 121.

Clarke, F. W., estimate of mass of sediments, 9; age of Earth by
sodium collection, 14; average composition of sedimentary and
igneous rocks, 42; on average composition of the crust, 126;
solvent denudation of the continents, 17, 40.

Claus, protoplasm the test of the cell, 67; abortion of useless
organs, 69.

Coefficient of friction, definition of, 262; deduction of, from
angle of friction, 263; abnormal values on ice, 261-265, 282; for
various substances, 265.

Continental areas, movements of, 144.

Cornil and Babes, size of spores, 98.

Croll, James, dawn of evolution, 301.

Crust of the Earth, average composition of, 126; depth of
softening in, 128.

Curie, definition of the, 256.

D.

Dana, on mountain building, 120.

Dawson, reduction of surface represented by Laramide range, 123.

Deccan traps, 137

_déferlement_, theory of, 155; explanation of, 155 _et seq._;
temperature involved in, 156.

Deimos, dimensions of, 177; orbit of, 577.

De Lapparent, exotic nature of the Préalpes, 150.

De Montessus and the association of earthquakes with
geosynclines, 142.

Denudation as affected by continental elevation, 17; factors
promoting, 30 _et seg._; relative activity in mountains and on
plains, 35-40; solvent, by the sea, 40; the sodium index of,
46-50; thickness of rock-layer removed from the land, 51.

De Quincy, System of the Heavens, 200.

Dewar, Sir James, latent image formed at low temperatures, 202.

Dixon, H. H., and AGnadance of Life, 60.

Double canals, formation by attraction of a satellite, 585-187.

Douglass, A. E., observations on Mars, 167.

Dravidian Era of India, 135.

E.

Earth, early history of, 3, 4; dimensions of, relative to surface
features, 117.

Earth's age determined by thickness of sediments, 5; determined
by mass of the sediments, 7; determined by sodium in the ocean,
12; determined by radioactive transformations, 19; significance
of, 2.

Earthquakes associated with geosynclincs, 142.

Efficiency, tendency to maximum, in organisms, 113, 114.

Elements, probable wide diffusion of rare, 230; rarity of
radioactive, 241.

Elster and Geitel, photo-electric activity and absorption, 207;
photo-electric properties of gelatin, 212; Emanation of radium,
therapeutic use of, 256-259; advantages of, in medicine, 256;
volume of, 257; how obtained, 257; use of, in needles, 258.

Equilibrium amount, meaning of, 254, 255.

Evolution and acceleration of activity, 79; of the universe not
eternal a pane ante, 298.

F.

Faraday and ionisation, 57.

Finality of progress a part, post, 289.

Flahault, experiments on colour of flowers, 108.

Fletcher, A. L., proportionality of thorium and uranium, 26,

G.

Galileo, discovery of Jupiter's moons, 162.

Gamma rays, nature of, 247: production of, by beta rays, 247; as
ionising agents, 249.

Geddes and Thomson, hunger and living matter, 71.

Geiger, range of alpha rays in air, 215; ionisation affected by
alpha rays in air, 216; on "scattering," 217; scattering and the
structure of the halo, 232.

Geikie, Sir A., uniformity in geological history, 15.

Geosynclines, 119; association with earthquakes and volcanoes,
142; of the tethys, 142; radioactive heat in, due to sediments,
130; temperature effects due to lateral compression of, 131.

Glacial epoch, phenomena of, 287.

Glacier motion, cause of. 285.

Glossopteris and Gangamopteris flora, 136.

Gondwanaland, 136.

Gradient of temperature in Earth's surface crust, 126.

H.

Haimanta period of India, 135.

Halley, Edmund, finding age by saltness of ocean, 13.

Hallwachs, photo-electric activity and absorption, 207.

Haloes, pleochroic, finding age of rocks by, 21; due to uranium
and thorium families, 227; radii of, 227; over-exposed and
underexposed, 228; intimate structure of, 229 _et seq._;
artificial, 229; tubular, in mica, 230; extreme age of, 231;
effect of nucleus on structure of, 232; inference from spherical
form of, in crystals, 233; structure of, unaffected by cleavage,
235; origin of the name "pleochroic,"235; colouration due to
iron, 235; colouration not due to helium, 236; age Of, 236; slow
formation of, 237, 238; number of rays required to build, 237;
and age of the Earth, 238-241.

Hayden, H.H., geology of the Himalaya, 134, 138, 139.

Heat-tendency of the universe, 62.

Heat emission from the Earth's surface, 126; from average igneous
rock due to radioactivity, 126.

Helium and the alpha ray, 214, 222; colouration of halo not due
to, 236.

Hering, E., and physiological or unconscious memory, 111.

Herschel and Babbage theory of mountain building, 123.

Herschel, Sir W., on galaxy of milky way, 293.

Hertz, negative electrification discharged by light, 204.

Himalaya, geological history of, 134-139.

Hobbs, on association of earthquakes and geosynclines, 143.

Holmes, A., original lead in minerals, 20; age of Devonian, 21.

Horst concerned in Alpine _déferlement_, objections to, 156.

Hyperion, dimensions of, 177.

I.

Ice, melting of, by pressure, 267 _et seq._; expansion of water
in becoming, 267; lowering of melting-point by pressure, 267;
fall of temperature under pressure, 268 _et seq._; viscosity of,
284.

Igneous rocks, average composition of, 43.

Inanimate actions, dynamic conditions of, 61.

Inanimate systems, secondary effects in, 63-65; transfer of
energy into, 66.

Indian geology, equivalent nomenclature of, 139.

Initial recombination of ions due to alpha rays, 221, 222, 231;
and structure of the halo, 231.

Insect life in the higher Alps, 104, 105; destruction of, on the
Alpine snows, 106.

Ionisation by alpha ray, density of, 221; importance in chemical
actions, 250; in living cell, 250.

Ions, number of, produced by an alpha ray, 237.

Isostasy, 53; and preservation of continents, 53.

Ivy, inconspicuous blossoms of, 107; delay in ripening seed,
107.

K.

Kant and Laplace, material hypothesis of, does not account for
the past, 290.

Kelvin, Lord, experiment on effects of pressure on ice, 268-270.

Kleeman and Bragg. See Bragg.

Klopstock introduces skating into Germany, 273.

L.

Lakes, cause of blue colour of, 55.

Land, movements of the, 53, 54.

Laukester, Ray, the soma and reproductive cells, 85.

Lapworth, structure of the Scottish Highlauds, 153.

Latent heat of water, 266.

Latent image, formed at low temperatures, 202; Bose's theory of,
203; photo-electric theory of, 204, 209 _et seq._

Least action, law of, 66.

Lembert and Richards, atomic weight of lead, 27.

Length of life dependent on conditions of structural development,
93; dependent on rate of reproduction, 94.

Life-curves of organisms having different activities, 92.

Life, length of, 91.

Life waves of a cerial, 95; of Ausaeba, 87; of a species, 90.

Light, effects of, in discharging negative electrification, 204;
chemical effects of, 205; experiment showing effect of, in
discharging electrified body, 205.

Lindemann, Dr., duration of solar heat, 29.

Lowell, Percival, observations on Mars, 167 _et seq._; map of
Mars, reliability of, 198.

Lucretius, birth-time of the world, 1.

Lugeon, formation of the Préalpes, 171; sections in the Alps,
154.

Lyell, uniformity in geological history, 15.

M.

Magee, relative areas of deposition and denudation, 16.

Mars, climate of, 170; position in solar system, 174, 175;
dimensions of satellites of, 177; snow on, 169; water on, 169;
clouds on, 169; atmosphere of, 170; melting of snow on, 170;
dimensions of canals, 171; signal on, 172; times of opposition,
164; orbit of, 165; distance from the Earth, 165; eccentricity of
his orbit, 165; observations of, by Schiaparelli, 165, 166;
Lowell's observations on, 167 _et seq._

Maxwell, Clerk, changes made under constraints, 65; on
conservation of energy, 61.

M'Connel, J. C., viscosity and rigidity of ice, 284.

Memory, physiological, 111, 112.

Metamorphism, thermal, in Alpine rocks, 132, 149

Millicurie, definition of, 256.

Molasse, accumulations of, 148.

Morin, coefficients of friction, 265.

Morphy, H., experiments on coefficient of friction of ice, 281.

Mountain-building and the geosynclines, 119-121; conditioned by
radioactive energy, 125; energy for, due to gravitation, 122;
reduction of surface attending, 123; depression attending, 123;
instability due to thermal effects of compression, 132; igneous
phenomena attending, 132; rhythmic character of, accounted for,
133; movements confined to upper crust, 122; movements due to
compressive stresses in crust, 122; movements, rhythmic character
of, 121.

Mountain ranges built of sedimentary materials, 118.

Müller, J., coefficient of friction of skate on ice, 265, 274.

Muth deposits of India, 135.

N.

Newton, Professor, of Yale, on origin of Mars' satellites, 177.

Nucleus, dimensions of, 237; amount of radium in, 238.

Nummulitic beds of Himalaya, 138.

O.

Ocean, amount of rock salt in, 50; cause of black colour of, 55;
estimated mass of sediments in, 48; increase of bulk due to
solvent denudation, 52; its saltness due to denudation, 41.

Old age and death, 82-85; not at variance with progressive
activity, 83.

Organic systems, origin of, 78.

Organic vibrations, 86 _et seq._

Organism and accelerative absorption of energy, 79; and economy,
109-111; and periodic rigour of the environment, 94,95.

Organism and sleep, 95; ultimate explanation of rythmic events
in, 96, 97; law of action of, 68 _et seq._; periodicity of; and
law of progressive activity, 82 _et seq._

P.

Penjal traps, 135.

Pepys and skating, 273.

Perry, coefficient of friction of greased surfaces, 265.

Phobos, dimensions of, 177; orbit of, 177.

Photoelectric activity and absorption, 207; persists at low
temperatures, 208, 209; not affected by solution, 213.

Photo-electric experiment, 205; sensitiveness of the hands, 207;
theory of latent image, 204, 209 _et seq._

Photographic reversal, experiments on, by Wood, 211; theory of,
210.

Piazzi, discovery of first Asteroid, 175.

Pickering, W. H., observations on Mars, 167.

Planet, slowing of axial rotation of, 189.

Plant, expectant attitude of, 109.

Pleochroic haloes, measurements of, 224; theory of, 224 _et
seq._; true form of, 226; radius of, and the additive law, 225;
absence of actinium haloes, 225; see _also_ Haloes; mode of
occurrence of, 223 _et seq._

Poole, J. H. J., proportionality of thorium and uranium, 26.

Poulton, uniformity of past climate, 17.

Pratt, Archdeacon, and isostasy, 53.

Préalpes, exotic nature of, 150, 151.

Prematerial universe, nature of a, 297, 300.

Prestwich and thickness of rigid crust, 128; history of the
Pyrenees, 140.

Primitive organisms, interference of, 89; life-curves of, 88.

Proctor and orbits of Asteroids, 176.

Protoplasm, encystment of, 68.

Purana Era of India, 134.

Pyrenees, history of, 140.

R.

Radioactive elements concerned in mountain building, 125.

Radioactive layer, failure to account for deep-seated
temperatures, 127; assumed thickness of, 128; temperature at base
of, due to radioactivity, 129; in the upper crust of the Earth,
125; thickness of, 126-128.

Radioactive treatment, physical basis of, 251.

Radioactivity and heat emission from average igneous rock, 126;
rarity of, established by haloes, 241, 243.

Radium, chemical nature and transmutation of, 244-245; emanation
of, 245; rays from, 253, 254; table of family of, 253; period of,
253; small therapeutic value of, 254.

Radium C, therapeutic value of, 254; rays from. 254; generation
of, 254.

Rationality, conditions for development of, 163.

Rays, similarity in nature of gamma, X, and light rays, 248;
effects on living cell, 251; penetration of, 251.

Reade, T. Mellard, finding age of ocean by calcium sulphate, 13.

Recumbent folds, formation of, 155 _et seq._

Regelation, 284; affecting glacier motion, 285.

Reversal, photographic, explanation of, 211.

Richards and Lembert, atomic weight of lead, 27.

Richter, Jean Paul, Dream of the Universe, 200.

Rock salt in the ocean, amount of, 13.

Rocks, average composition of, 43; radioactive heat from, 126;
rate of solution of, 36.

Russell, I. C., river supply of sediments, 10.

Rutherford, Sir E., determination of age of minerals, 19, 20; age
of rocks by haloes, 22; derivation of actinium, 226; artificial
halo, 229; number of alpha rays from one gram of radium, 237.

S.

Salt range deposits of India, 134. 135.

Saltness of the ocean due to denudation, 41-46.

Salisbury (and Chamberlin), the Larimide range, 121.

Salmon, Rev. George, on creation, 301.

Satellite, velocity of, in its orbit, 191; method of finding path
of, over a rotating primary, 189 _et seq._; direct and
retrograde, 178; ultimate end of, 178; path of, when falling into
primary, 179; effect of Mars' atmosphere on infalling satellite,
179; stability of close to primary, 180; effects of, on crust of
primary, 180 _et seq._

Schiaparelli, observations on Mars, 165 166.

Schmidt, C., original depth of Alpine layer, 131-148; structure
of the Alps, 152.

Schmidt, G. C., on photo-electricity, 207, 208; effect of
solution on photo-electric activity, 213.

Schuchert, C., average area of N. America during geological time,
16.

Sedimentary rocks, average composition of, 43; mass of,
determined by sodium index, 47.

Sedimentation a convection of energy, 133.

Sediments, average river supply of, 11; on ocean floor, mass of,
48; average thickness of, 49; precipitation of, by dissolved
salts, 56-58; radioactivity of 130; radioactive heat of,
influential in mountain building, 130, 131; rate of collecting,
7; determination of mass of, 8; river supply of, 10; total
thickness of, 6.

Semper, energy absorption of vegetable and animal systems, 78.

Sensitisers, effects of low temperature on, 210.

Simplon, radioactive temperature in rocks of, before denudation,
132.

Skates, early forms of, 273; principles of construction of, 273
_et seq._; action of, on ice, 276; bite of, 278-280.

Skating not dependent on smoothness of ice, 260; history of,
273.

Skating only possible on very few substances, 279.

Soddy, F., on isotopes, 24.

Sodium, deficiency of, in sediments, 44; discharge of rivers,
14.

Soils, formation of, 37-39; surface area exposed in, 39.

Sollas, W. J., age of Earth by sodium in ocean, 14; thickness of
sediments, 6.

Spencer, on division of protoplasm, 67.

Spores, number of molecules in, 97.

Stevenson, Dr. Walter C., and technique of radioactive treatment,
259.

Stoletow, photo-electric activity anal absorption, 207.

Stopping power of substances with reference to alpha rays, 219.

Struggle for existence, dynamic basis of, 80.

Strutt, Prof. the Hon. R. J., age of geological periods, 20;
radioactivity of zircon, 223.

Sub-Apennine series of Italy, 148.

Suess, nature of earthquakes. 143.

Survival of the fittest and the organic law, 80.

T.

Talchir boulder-bed, 136.

Temperature gradient in Earth's crust, 126.

Termier, section of the Pelvoux Massif, 254.

Tethys, early extent of, 135-137; geosynclines of, 142.

Thermal metamorphism in Alpine rocks, 132, 149.

Thomson, James, prediction of melting of ice by pressure, 267.

Thorium and uranium, proportionality of, in older rocks, 26.

Triple canals, formation of, by attraction of a satellite, 187.

Tyndall, colour of ocean water, 55.

U.

Uniformitarian view of geological history, 15-18.

Universe, simultaneity of the, 293-295.

Uranium-radium family of elements, table of, 253.

V.

Val d'Hérens, earth pillars of, 33.

Van Tillo, nature of continental rock covering, 9.

Vegetable and animal systems, relative absorption of energy of,
78.

Vegetative organs, struggle between, 105, 106.

Volcanoes and mountain ranges, 118; associated with geosynclines,
142; Oligocene and Miocene of Europe, 147.

W.

Weinschenk and thermal metamorphism, 132,

149.

Weismaun, encystment of protoplasm, 68; length of life and
somatic cells, 96; origin of death, 83; tendency to early
reproductiveness, 98.

Wilson, C. T. R., visualised alpha rays, 218.

Winchell, progressive changes of matter not eternal, 302.

Wood, R. W., on photographic reversal, 211.

Z.

Zircon, radioactivity of, 223; as nucleus of halo, 223.