450 Reviews—Browne’s Ice-caves of France and Switzerland. 
natural ice-caves, except that they did exist. The little that was 
known Mr. Browne made himself acquainted with, and then set out 
on his tour of examination of twelve glaciéres, the localities of which 
he had succeeded in discovering. ‘The general reader will find his 
narrative full of interesting adventure, and lively description of the 
scenes through which he passed, as well as of the wonders he found 
‘in the caves. For the man of science they contain many interesting 
facts and puzzling phenomena which must yet rest some time before 
they can be thoroughly understood and expounded. 
Ice-caves occur at depths varying from 50 to 200 feet below the 
surface of the earth, unconnected with glaciers or snow-mountains, 
and in latitudes and at altitudes where ice would not under ordinary 
circumstances be supposed to exist. ‘They are employed, when the 
artificial stores of ice are exhausted, to supply this now almost 
necessary luxury. ‘The ice is sometimes opayue, but frequently 
perfectly clear and transparent, and often formed into masses of 
the most beautiful or the most grotesque forms. We do not wonder 
that Mr. Browne, even with benumbed fingers and wet feet, crawl- 
ing on all-fours on slippery ice, gets occasionally into raptures with 
the wondrous scene suddenly revealed to his view by the light of 
his torch. 
The great difficulty with regard to these ice-caves or glaciéres, is 
to account for their existence. Our autkor, after recounting the 
numerous—many of them most absurd—theories which have been 
‘offered in explanation, gives one which to our mind is as unsatisfac- 
tory as any of the rest. It is, as he tells us, that of Deluce’s, but 
arrived at by himself independently. He thus states it:—‘ The 
heavy cold air of winter sinks down into the glacierés, and the 
lighter warm air of summer cannot on ordinary principles of gravi- 
tation 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 ice in the cave.’ We doubt if the air is so stable a 
body as this theory demands. Its power of conducting heat is also 
considerable. It is true that the airis always cold in the caves; but 
this is easily explained by the generally wet surface of the ice, which 
in melting absorbs so much heat. May not the earth rather than 
the air be the cause of the ice in the caves? ‘There are different 
temperature-layers in the earth’s crust, as they are affected by ex- 
ternal heat. First, there is the thin surface-layer, affected by the 
varying temperature of day and night. Then there is the season- 
temperature plane, varying with the uniformity of the seasons and 
the conducting power of the materials of the crust, being at the 
Equator only a foot below the surface, in the Arctic regions from 
3 to 12, while in the Temperate Zone it is 50 or 60 feet. Then 
there is the layer of climate temperature, where the summer's heat 
and the winter’s cold are alike unfelt: in the Temperate Zone this 
varies from 200 to 400 feet, and in the Arctic regions from 8 or 10 
to 90. Bélow this we have a plane of terrestrial temperature beyond 
