HISTORY OF THEORIES RESPECTING THE CAUSES OF SUBTERRANEAN ICE.
The only glacière which is in any sense historical, is that near
Besançon; and a brief account of the different theories which have been
advanced in explanation of the phenomena presented by it, will include
almost all that has been written on ice-caves.
The first mention I have found of this cave is contained in an old
history of the Franche Comté of Burgundy, published at Dôle in 1592, to
which reference has been already made. Gollut, the author, speaks more
than once of a _glacière_ in his topographical descriptions, and in a
short account of it he states that it lay near the village of _Leugné_,
which I find marked in the Delphinal Atlas very near the site of the
Chartreuse of Grâce-Dieu; so that there can be no doubt that his
glacière was the same with that which now exists. His theory was, that
the dense covering of trees and shrubs protected the soil and the
surface-water from the rays of the sun, and so the cold which was stored
up in the cave was enabled to withstand the attacks of the heat of
summer.[175] In the case of many of the glacières, there can be no
doubt that this idea of winter cold being so preserved, by natural
means, as to resist the encroachments of the hotter seasons, is the true
explanation of the phenomenon of underground ice.
The next account of this glacière is found in the History of the Royal
Academy of Sciences (French), under the year 1686,[176] but no theory is
there suggested. The writer of the account states that in his time the
floor of the cave was covered with ice, and that ice hung from the roof
in festoons. In winter the cave was full of thick vapours, and a stream
of water ran through it. The ice had for long been less abundant than in
former times, in consequence of the felling of some trees which had
stood near the entrance.
The Academy received in the same year another letter on this subject,
confirming the previous account, and adding some particulars. From this
it would seem that people flocked from all sides to the glacière with
waggons and mules, and conveyed the ice through the various parts of
Burgundy, and to the camp of the Saone; not thereby diminishing the
amount of ice, for one hot day produced as much as they could carry away
in eight days. The ice seemed to be formed from a stream which ran
through the cave and was frozen in the summer only. The writer of this
second account saw vapours in the glacière (the editor of the _Histoire
de l'Académie_ does not say at what season the visit to the cave took
place), and was informed that this was an infallible sign of approaching
rain; so much so, that the peasants were in the habit of determining the
coming weather by the state of the grotto.
In 1712, M. Billerez, Professor of Anatomy and Botany in the University
of Besançon, communicated to the Academy[177] an account of a visit made
by him to this cave in September 1711. He found 3 feet of ice on the
floor of the cave, in a state of incipient thaw, and three pyramids,
from 15 to 20 feet high and 5 or 6 feet in diameter, which had been
already considerably reduced in size by thaw. A vapour was beginning to
pass out from the cave, at the highest part of the arch of entrance; a
phenomenon which, he was told, continued through the winter, and
announced or accompanied the departure of the ice: nevertheless, the
cold was so great that he could not remain in the glacière more than
half an hour with any sort of comfort. The thermometer stood at 60°
outside the cave, and fell to 10°[178] when placed inside; but
thermometrical observations of that date were so vague as to be useless
for present purposes. The ice appeared to be harder than the ordinary
ice of rivers, less full of air-bubbles, and more difficult to melt.
M. Billerez enunciated a new theory to account for the phenomena
presented by the cave. He observed that the earth in the immediate
neighbourhood, and especially above the roof of the grotto, was full of
a nitrous or ammoniac salt, and he accordingly suggested that this salt
was disturbed by the heat of summer and mingled itself with the water
which penetrated by means of fissures to the grotto, and so the cave was
affected in the same way as the smaller vessel in the ordinary
preparation of artificial ice. He had heard that some rivers in China
freeze in summer from the same cause.[179]
In 1726, a further communication was made to the Academy by M. des
Boz,[181] Royal Engineer, describing four visits which he had made to
the grotto near Besançon at four different seasons of the year, viz., in
May and November 1725, and in March and August 1726. In all cases he
found the air in the cave colder than the external air,[182] and its
variations in temperature corresponded with the external variations, the
cold being greater in winter than in summer.
M. des Boz ascribed the existence of ice in the cave to natural causes.
The opening being towards the north-east, and corresponding with a gorge
in the hills opposite, running in the same direction, none but cold
winds could reach the mouth of the grotto. Moreover, the soil above was
so thickly covered with trees and brushwood, that the rays of the sun
could not reach the earth, much less the rock below. Credible persons
asserted that since some of the trees had been felled, there had not
been so much ice in the cave.
In order to test the presence of salt, M. des Boz melted some of the
ice, and evaporated the resulting water, but found no taste of salt in
the matter which remained.[183] He denied the existence of the spring of
water which previous accounts had mentioned, and believed that the water
which formed the ice came solely from melted snow, and from the
fissures of the rock.
In 1727, the Duc de Lévi caused the whole of the ice to be removed from
the cave, for the use of the army of the Saone, which he commanded. In
1743 the ice had formed again, and the grotto was subjected to a very
careful investigation by M. de Cossigny, chief engineer of Besançon, in
the months of August and October.[183] The thermometer he used had been
presented to him by the Academy, and was very probably constructed by M.
de Réaumur himself, for de Cossigny's account was sent through M. de
Réaumur to the Academy, but still the observations made with it cannot
be considered very trustworthy. On the 8th of August, at 7.30 A.M., the
temperature in the cave was 1/2° above the zero point of this
thermometer, and at 11.30 A.M. it had risen to 1° above zero. On the
17th of October, at 7 A.M., the thermometer stood at 1/2°, and at 4 P.M.
it gave the same register.
M. de Cossigny found that the entrance to the cave was rather more than
150 feet above the Abbey of Grâce-Dieu, and about half a league distant
by the ordinary path. A great part of his account is occupied by
contradictions of previous accounts, especially in the matter of
dimensions,[184] The people of Besançon had urged him to stay only a
short time in the cave, because of the sulphureous and nitrous
exhalations, but he detected no symptoms of anything of that kind. The
most curious thing which he saw was the soft earth which lay, and still
lies, at the bottom of the long slope of ice by which the descent is
made; and he subjected this to various chemical tests and processes, but
could not find that it contained anything different from ordinary
earth.[185]
When M. de Cossigny visited the cave, there were thirteen or fourteen
columns of ice, from 6 to 8 feet high, and he was in consequence
inclined to doubt the accuracy of the statement of M. Billerez, that in
his time (1711) there were three columns only, from 15 to 20 feet high.
But my own observation of the shape of the columns suggested that the
largest of all was probably an amalgamation of several others; so that
it is not unreasonable to suppose that after the Duc de Lévi removed the
large columns seen by M. Billerez, a number of smaller columns were
formed on the old site, and that these had not become large enough to
amalgamate in 1743.
Not satisfied with these visits of August and October, M. de Cossigny
visited the cave in April 1745. He found the temperature at 5 A.M. to be
exactly at the freezing point, and at noon it had risen 1°. From this he
concluded that the stories of the greater cold in the cave during the
summer, as compared with the winter, were false.
In 1769, M. Prévost, of Geneva, visited the cave, as a young man; and in
1789, he wrote an account of his visit in the _Journal de Genève_
(March), which was afterwards inserted as an additional chapter in his
book on Heat.[186] He believed that one or two hundred _toises_ was the
utmost that could be allowed for the height of the hill in which the
glacière lies,--a sufficiently vague approximation. He rejected the idea
of salt as the cause of ice, and came to the conclusion that the cave
was in fact nothing more than a good natural ice-house, being protected
by dense trees, and a thick roof of rock, while its opening towards the
north sheltered it from all warm winds. He accounted for the original
presence of ice as follows:--In the winter, stalactites form at the
edges of various fissures in the roof, and snow is drifted on to the
floor of the cave by the north winds down the entrance-slope. When the
warmer weather comes, the stalactites fall by their own weight, and,
lying in the drifted and congealed snow, form nuclei round which the
snow is still further congealed, and the water which results from the
partial thaw of portions of the snow is also converted into ice. Thus, a
larger collection of ice forms in winter than the heat of summer can
destroy; and if none of it were removed, it might, in the course of
years, almost fill the cave. At the time of his visit (August), M.
Prévost found only one column, from 6 to 8 feet high.
In 1783 (August 6), M. Girod-Chantrans visited the Glacière of Chaux
(so called from a village near the glacière, on the opposite side from
the Abbey of Grâce-Dieu), and his account of the visit appeared in the
_Journal des Mines_[187] of Prairial, an iv., by which time the writer
had become the Citizen Girod-Chantrans. He found a mass of
stalactites of ice hanging from the roof, as if seeking to join
themselves with corresponding stalagmites on the floor of the cave;
the latter, five in number, being not more than 3 or 4 feet high, and
standing on a thick sheet of ice. There was a sensible interval
between this basement of ice and the rock and stones on which it
reposed: it was, moreover, full of holes containing water, and the
lower parts of the cave were unapproachable by reason of the large
quantity of water which lay there. The thermometer stood at 35°·9 F.
two feet above the floor, and at 78° F. in the shade outside. M.
Girod-Chantrans determined, from all he saw and heard, that the summer
freezing and winter thaw were fables, and he believed that the cave
was only an instance of Nature's providing the same sort of receptacle
for ice as men provide in artificial ice-houses. He was fortunate
enough to obtain by chance the notes of a neighbouring physician, who
had made careful observations and experiments in the glacière at
various seasons of the year, and a _précis_ of these notes forms the
most valuable part of his account.
Dr. Oudot, the physician in question, found ten columns in January 1778,
the largest of which was 5-1/2 feet high. The flooring of ice was
nowhere more than 15 inches thick, and the parts of the rock which were
not covered with ice were perfectly dry. The thermometer--M.
Girod-Chantrans used Réaumur, so I suppose that he gives Dr. Oudot's
observations in degrees of Réaumur, though some of the results of that
supposition appear to be anomalous--gave 22° F. within the cave, and 21°
F. outside.
In April of the same year, the large column had increased in height to
the extent of 13 inches; and the floor of ice on which it stood was
1-1/2 inch thicker, and extended over a larger area than before; the
thermometer stood at 36°.5 F. and 52° F. respectively in the same
positions as in the former case. In July, the large column had lost 6
inches of its height, and the thermometer gave 38°.75 F. and 74°.75 F.
In October, the large column was only 3 feet high, and many of the
others had disappeared, while their pedestal had become much thinner
than it had been in the preceding months. There was also a considerable
amount of mud in the cave, brought down apparently by the heavy rains of
autumn. The thermometer gave 37°.6 F. and 63°.5 F.
On the 8th of January, 1779, there were nine columns of very beautiful
ice, and one of these, as before, was larger than the rest, being 5 feet
high and 10 feet in circumference. The temperatures were 21° F. and
16°.15 F. in the cave and in the open air respectively.
Tradition related that, before the removal of the ice in 1727, one of
the columns reached the roof, (Prévost calculated the limits of the
height of the cave at 90 and 60 feet,) and this suggested to Dr. Oudot
the idea of placing stakes of wood in the heads of the columns he found
in the cave, in the hope that ice would thus collect in greater
quantities under the fissures of the roof. Accordingly, he made holes in
three of the columns, and established stakes 4, 5, and 10 feet high,
returning on the 22nd of February, after an interval of six weeks, to
observe the result of his experiment. He found the two shorter stakes
completely masked with ice, forming columns a foot in diameter; and the
longest stake, though not entirely concealed by the ice which had
collected upon it, was crowned with a beautiful capital of perfectly
transparent ice. The columns which had no stakes fixed upon them had
also increased somewhat in size, but not nearly in the same proportion
as those which were the subject of Dr. Oudot's experiment. The
thermometer on this day gave 29°.5 F. and 59° F. as the temperatures.
It may be remembered that I found one very beautiful column, far higher
than any of those mentioned by Dr. Oudot, and higher than those which M.
Billerez saw, formed upon the trunk and branches of a fir-tree. I have
now no doubt that the peculiar shape of another--the largest of the
three columns which were in the cave at the time of my visit--is due to
the fact of its being a collection of several smaller columns, which
have in course of time flowed into one as they increased separately in
bulk, and that its height has been augmented by a device similar to that
adopted by Dr. Oudot. The two magnificent capitals which this column
possessed, as well as the numerous smaller capitals which sprang from
its sides, will thus be completely accounted for.
One more account may be mentioned, before I proceed to the theory which
has found most favour in Switzerland of late years. M. Cadet published
some _Conjectures_ on the formation of the ice in this cavern, in the
_Annales de Chimie,_ Nivôse, an XI.[188] He saw the cave in the end of
September 1791, and found very little ice--not a third of what there had
been a month before, according to the account of his guide. The
_limonadier_ of a public garden in Besançon informed him that the people
of that town resorted to the glacière for ice when the supplies of the
artificial ice-houses failed, and that they chose a hot day for this
purpose, because on such days there was more ice in the cave. Ten
_chars_ would have been sufficient to remove all the ice M. Cadet found,
and the air inside the cave seemed to be not colder than the external
air; but, nevertheless, M. Cadet believed the old story of the greater
abundance of ice in summer than in winter, and he attempted to account
for the phenomenon.
The ground above and near the cave is covered with beech and chestnut
trees, and thus is protected from the rays of the sun. The leaves of
these trees give forth abundant moisture, which has been pumped up
from their roots; and as this moisture passes from the liquid to the
gaseous state, it absorbs a large quantity of caloric. Thus,
throughout the summer, the atmosphere is incessantly refrigerated by
the evaporation produced by the trees round the cave; whereas in
winter no such process goes on, and the cave assumes a moderate
temperature, such as is usually found in ordinary caves. Unfortunately
for M. Cadet's theory, the facts are not in accordance with his
imaginary data, nor yet with his conclusions. He adds, on the
authority of one of his friends, that the intendant of the province,
M. de Vanolles, wishing to preserve a larger amount of ice in the
cave, built up the entrance with a wall 20 feet high, in which a small
door was made, and the keys were left in the hands of the authorities
of the neighbouring village, with orders that no ice should be
removed. The effect of this was, that the ice diminished considerably,
and they were obliged to pull down the wall again. M. Cadet saw the
remains of the wall, and the story was confirmed by the Brothers of
Grâce-Dieu. It would be very interesting to know at what season this
wall was built, and when it was pulled down. If my ideas on the
subject of ice-caves are correct, it would be absolutely fatal to shut
out the heavy cold air of winter from the grotto.
In 1822, M.A. Pictet, of Geneva, took up the question of natural
glacières, and read a paper before the Helvetic Society of Natural
Sciences,[189] describing his visits to the caves of the Brezon and the
Valley of Reposoir. In order to explain the phenomena presented by those
caves, M. Pictet adopted De Saussure's theory of the principle of
_caves-froides_, rendering it somewhat more precise, and extending it
to meet the case of ice-caves. It is well known that, in many parts of
the world, cold currents are found to blow from the interstices of
rocks; and these are utilised by neighbouring proprietors, who build
sheds over the fissures, and so secure a cool place for keeping meat,
&c. Examples of such currents are met with near Rome (in the _Monte
Testaceo_), at Lugano, Lucerne (the caves of Hergiswyl), and in various
other districts. It is found that the hotter the day, the stronger is
the current of cold air; in winter the direction of the current is
changed, and it blows into the rock instead of out from it.[190] De
Saussure's theory, as developed by M. Pictet, was no doubt satisfactory,
so far as it was used to account for the phenomenon of 'cold-caves,' but
it seems to be insufficient as an explanation of the existence of large
masses of subterranean ice; of which, by the way, De Saussure must have
been entirely ignorant, for he makes no allusion to such ice, and the
temperatures of the coldest of his caves were considerably above the
freezing point.
Pictet represents the case of a cave with cold currents of air to be
much the same as that of a mine with a vertical shaft, ending in a
horizontal gallery of which one extremity is in communication with the
open air, at a point much lower, of course, than the upper extremity of
the shaft. The cave corresponds to the horizontal gallery, and the
various fissures in the rock take the place of the vertical shaft, and
communicate freely with the external air. In summer, the columns of air
contained in these fissures assume nearly the temperature of the rock in
which they rest, that is to say, the mean temperature of the district,
and therefore they are heavier than the corresponding external columns
of air which terminate at the mouth of the cave; for the atmosphere in
summer is very much above the mean temperature of the soil, or of the
interior of the earth at moderate depths. The consequence is, that the
heavy cool air descends from the fissures, and streams out into the
cave, appearing as a cold current; and the hotter the day is--that is,
the lighter the columns of external air--the more violent will be the
disturbance of equilibrium, and therefore the more palpable the cold
current. Naturally, in this last case, the air which enters by the upper
orifices of the fissures is more heated, to begin with, than on cooler
days; but external heat so very slightly affects the deeper parts of the
fissures, that the columns of air thus introduced are speedily impressed
with the mean temperature of the district. In winter, the external
columns of air are as much heavier than the columns in the fissures as
they are lighter in summer; and so cold currents of air blow from the
cave into the fissures, though such currents are not of course colder
than the external air. Thus the mean temperature of the cave is much
lower than that of the rock in which it occurs; for the temperature of
the currents varies from the mean temperature of the rock to the winter
temperature of the external atmosphere.
The descending columns of warmer air, in summer, must to some extent
raise the temperature of the fissures above that which they would
otherwise possess, that is, above the mean temperature of the place; but
that may be considered to be counteracted by the corresponding lowering
of the temperature of the fissures by the introduction of cold air from
the cave in winter. By a similar reasoning, it will be seen that for
some time after the spring change of direction in the currents takes
place, the temperature of the cave will be less than would have been
expected from a calculation founded on the true mean temperature of the
rock through which the fissures pass. This, together with the fact of
the porous nature of the rock in which most of the curious caves in the
world occur, which allows a considerable amount of moisture to collect
on all surfaces, and thereby induces a depression of temperature by
evaporation, may be held to explain the presence of a greater amount of
cold than might otherwise have been fairly reckoned upon in ice-caves.
The idea of cold produced by evaporation Pictet took up warmly,
believing that when promoted by rapid currents of air it would produce
ice in the summer months; and he thus explained what he understood to be
the phenomena of glacières. But it will have been seen, from the account
of the caves I have visited, that the glacières are more or less in a
state of thaw in the summer; and M. Thury's observations in the winter
prove conclusively that they are then in a state of utter frost, so that
the old belief with respect to the season at which the ice is formed may
be supposed to have been exploded. The facts recorded by Mr. Scrope[191]
would appear to depend upon the peculiar nature of rocks of volcanic
formation; and I am inclined to think there is very little in common
between such instances as he mentions and the large caves filled with
ice which are to be found in the primary or secondary limestone.
One of De Saussure's experiments, in the course of his investigation of
the phenomena and causes of cold currents in caves, is worth recalling.
He passed a current of air through a glass tube an inch in diameter,
filled with moistened stones, and by that means succeeded in reducing
the temperature of the current from 18° C. to 15° C.; and when the
refrigerated current was directed against a wet-bulb thermometer, it
fell to 14° C., thus showing a loss of 7°·2 F. of heat. No one can see
much of limestone caverns without discovering that the surfaces over
which any currents there may be are constrained to pass, present an
abundance of moisture to refrigerate the currents; and it is not
unreasonable to suppose that the large number of evaporating surfaces,
which currents passing through heaps of débris--such as the basaltic
stones described on page 261--come in contact with, are the main cause
of the specially low temperature observed under such circumstances.
Pictet's theory, however, did not convince all those into whose hands
his paper fell, and M.J. Deluc wrote against it in the _Annales de
Chimie et de Physique_ of the same year, 1822.[192] Deluc had not seen
any glacière, but he was enabled to decide against the cold-current
theory by a perusal of Pictet's own details, and of one of the accounts
of the cave near Besançon. He objected, that in many cases the ice is
found to melt in summer, instead of forming then; and also, that in the
Glacière of S. Georges, which Pictet had described, there was no current
whatever. Further, in all the cases of cold currents investigated or
mentioned by De Saussure, the presence of summer ice was never even
hinted at, and the lowest temperatures observed by him were considerably
above the freezing point. I may add, from my own experience, that on the
only occasions on which I found a decided current in a glacière--viz.,
in the Glacière of Monthézy, and that of Chappet-sur-Villaz,--there was
marked thaw in connection with the current. In the latter case, the
channel from which the current came was filled with water; and in the
former, water stood on the surface of the ice.
The view which Deluc adopted was one which I have myself independently
formed; and he would probably have written with more force if he had
been acquainted with various small details relating to the position and
surroundings of many of the caves. The heavy cold air of winter sinks
down into the glacières, and the lighter warm air of summer cannot on
ordinary principles of gravitation dislodge it, so that heat is very
slowly spread in the caves; and even when some amount of heat does reach
the ice, the latter melts but slowly, for ice absorbs 60° C. of heat in
melting; and thus, when ice is once formed, it becomes a material
guarantee for the permanence of cold in the cave.
For this explanation to hold good, it is necessary that the level at
which the ice is found should be below the level of the entrance to the
cave; otherwise the mere weight of the cold air would cause it to leave
its prison as soon as the spring warmth arrived. In every single case
that has come under my observation, this condition has been emphatically
fulfilled. It is necessary, also, that the cave should be protected from
direct radiation, as the gravitation of cold air has nothing to do with
resistance to that powerful means of introducing heat. This condition,
also, is fulfilled by nature in all the glacières I have visited,
excepting that of S. Georges; and there art has replaced the protection
formerly afforded by the thick trees which grew over the hole of
entrance. The effect of the second hole in the roof of this glacière is
to destroy all the ice which is within range of the sun. A third and
very necessary condition is, that the wind should not be allowed access
to the cave; for if it were, it would infallibly bring in heated air, in
spite of the specific weight of the cold air stored within. It will be
understood from my descriptions of such glacières as that of the Grand
Anu, of Monthézy, and the Lower Glacière of the Pré de S. Livres, how
completely sheltered from all winds the entrances to those caves are.
There can be no doubt, too, that the large surfaces which are available
for evaporation have much to do with maintaining a somewhat lower
temperature than the mean temperature of the place where the cave
occurs. This had been noticed so long ago as Kircher's time; for among
the answers which his questions received from the miners of Herrengrund,
we find it stated that, so long as mines are dry, the deeper they are
the hotter; but if they have water, they are less warm, however deep.
From the mines of Schemnitz he was informed that, so long as the free
passage of air was not hindered, the mines remained temperate; in other
cases they were very warm. Another great advantage which some glacières
possess must be borne in mind, namely, the collection of snow at the
bottom of the pit in which the entrance lies. This snow absorbs, in the
course of melting, all heat which strikes down by radiation or is driven
down by accidental turns of the wind; and the snow-water thus forced
into the cave will, at any rate, not seriously injure the ice. It is
worthy of notice that the two caves which possess the greatest depth of
ice, so far as I have been able to fathom it, are precisely those which
have the greatest deposit of snow; and the ice in a third cave, that of
Monthézy, which has likewise a large amount of snow in the entrance-pit,
presents the appearance of very considerable depth. The Schafloch, it is
true, which contains an immense bulk of ice, has no snow; but its
elevation is great, as compared with that of some of the caves, and
therefore the mean temperature of the rock in which it occurs is less
unfavourable to the existence of ice.
I believe that the true explanation of the curious phenomena presented
by these caves in general, is to be found in Deluc's theory, fortified
by such facts as those which I have now stated. The mean temperature of
the rock at Besançon, where the elevation above the sea is
comparatively so small, renders the temptation to suggest some chemical
cause very strong.
The question of ice in summer where thaw prevails in winter, may fairly
be considered to have been eliminated from the discussion of such caves
as I have seen, in spite of the persistent assertions of some of the
peasantry. The observations, however, in caverns in volcanic formations,
and in basaltic débris, are so circumstantial that it is impossible to
reject them; and in such cases a theory similar to that enunciated by
Mr. Scrope[193] seems to be the only one in any way satisfactory, though
I have not heard of such marvellous results being produced elsewhere by
evaporation. One observer, for instance, of the cavern near the village
of Both, in the Eiffel, found a thickness of 3 feet of ice; and in that
case it was melting in summer, instead of forming. In some cases it has
been suggested that the length of time required for external heat or
cold to penetrate through the earth and rock which lie above the caves
is sufficient to account for the phenomenon of summer frost and winter
thaw. Thus, it is said, the thickness of the superincumbent bed may be
such that the heat of summer only gets through to the cave at Christmas,
and then produces thaw, while in like manner the greatest cold will
reach the cave in mid-summer. But there is a fatal objection to this
idea in the fact that the invariable stratum--i.e., the stratum beyond
which the annual changes of external temperature are not felt--is
reached about 60 feet below the surface in temperate latitudes,[194]
while at the tropics such changes are not felt more than a foot below
the surface. Humboldt calculated that in the latitude of central France
the whole annual variation in temperature at a depth of 30 feet would
not amount to more than one degree.[195]
FOOTNOTES:
[Footnote 174: As Gollut's phraseology is peculiar, it may be as well
to reproduce his account of the cave:--'Je ne veux pas omettre
toutefois (puisque je suis en ces eaux) de mettre en memoire la
commodité que nature hat doné à quelques delicats, puis qu'au fond
d'un mõntagne de Leugné, la glace (_glasse_ in the index), se treuve
en esté, pour le plaisir de ceux qui aim[~e]t a boire frais. Néanmoins
dans ce t[~e]ps cela se perd, nõ pour autre raison (ainsi que íe
pense) que pour ce que lon hat dépouillé le dessus de la mõtagne d'une
époisse et aulte fustaie de bois, qui ne permettoit pas que les raions
du soleil vinsent échauffer la terre et déseicher les distillations,
que se couloi[~e]t iusques au plus bas et plus froid de la montagne:
ou (par l'antipéristase) le froid s'epoississoit, et se reserroit,
contre les chaleurs, entornantes et environnantes le long de l'esté,
toute la circonference extérieure du mont.'--_Histoire_, &c., p. 87.]
[Footnote 175: _Hist. de l'Acad._, t. ii., p. 2.]
[Footnote 176: _Hist. de l'Acad._, an 1712, p. 20.]
[Footnote 177: _C'est à dire_--M. Billerez explains--_à 10 degrés
au-dessous du très-grand froid._ What the 60° may be worth, I cannot
say.]
[Footnote 178: Tournefort (_Voyage du Levant_, iii. 17) believed that
the ammoniac salt, of which the earth was full in some districts near
Erzeroum, had something to do with the persistence of snow on the ground
there.]
[Footnote 179: _Hist, de l'Acad.,_ an 1726, p. 16.]
[Footnote 180: But see on this point the experience of M. Thury, in the
Glacière of S. Georges (Appendix).]
[Footnote 181: Sir Roderick Murchison's suggestion of the possible
influence of salt in producing the phenomena of his ice-cave in Russia,
did not, of course, proceed upon the supposition of salt actually
mingling with water, but only of its increasing the evaporation of the
air which came in contact with it.]
[Footnote 182: _Mém. présentés à l'Académie par divers Sçavans_, i,
195.]
[Footnote 183: A long account was published in a history of Burgundy,
printed at Dijon, in quarto, in 1737, which I have not been able to
find. It was from the same source as the account in the Hist. of the
Academy, in 1726.]
[Footnote 184: I took this earth to be a collection of the particles
carried down the slope of ice by the heavy rains of the month preceding
my visit. M. de Cossigny speaks of the abundant rains of July, his visit
being in August.]
[Footnote 185: _Recherches sur la Chaleur_; Geneva and Paris, 1792.]
[Footnote 186: P. 65. Now called _Annales des Mines_.]
[Footnote 187: T. xlv. p. 160.]
[Footnote 188: _Bibliothèque Universelle de Genève_, Première Série, t.
xx.]
[Footnote 189: See De Saussure's account of his numerous observations of
such caves in the _Voyage dans les Alpes_, sections 1404-1415.]
[Footnote 190: P. 271.]
[Footnote 191: P. 271.]
[Footnote 192: xxi. 113.]
[Footnote 193: P. 271.]
[Footnote 194: Daubuisson estimated the depth in question at from 46 to
61 feet, while Kupffer put it at 77 feet.]
[Footnote 195: De Saussure found a variation of 2°·25 F. at a depth of
29·5 feet; but this was in a well, where the influence of the atmosphere
was allowed to have effect. Naturally, the fissures which there may be
in the rock surrounding a cave will increase the annual variation of
temperature, by affording means of easier penetration to the heat and
cold.
Sir K. Murchison's cavern in Russia would seem to be entirely _sui
generis_.]
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