FREEZING CAVERN AT ILLETZKAYA-ZASTCHITA. 
191 
sum both when open from its summit and without such aperture ? Is it, on the con- 
trary, a phenomenon which changes with the seasons, as the inhabitants declare? 
If so, is it susceptible of explanation by climatological changes, as attempted by 
Sir John Herschel? or is it to be accounted for by an union of meteorological 
and chemical causes ? Avowing our incompetency to explain the true nature 
of the changes by which the result was produced, we were about to state, that in 
clinging to our original belief, or some modification of it, we left the problem to 
be solved by others. Whilst, however, these pages were passing through the press, 
the facts having been accidentally mentioned to our friend Dr. Robinson 1 , he ex- 
pressed an opinion which induced us to elicit from him the following ingenious 
explanation : — 
“ Your revise lias reached me, where I am luckily able to refer to the account of Monte Testaceo 
which I mentioned to you at Parsonstown, and which you will find in the first volume of Nicholson’s 
Journal, 4to series, page 229. If you examine it, you will, I think, agree with me in thinking that the 
principles applied by Nicholson to explain these phamomena, nearly as you appear to have done in the 
first instance, are sufficient forllletzkaya.” “ First suppose the hill rifted with fissures so as 
to let air percolate all through it, and that this net-work of air-passages communicates with the cave 
below, and above with vertical fissures communicating towards the summit of the hill with the external 
atmosphere. During winter the air contained in these fissures is warmer than that without, it will there- 
fore rise and escape, being replaced by an equal mass of cold air. This being warmed by the rock with 
which it is in contact, will escape in its turn, and thus an inward current will be felt in the cave till all 
the rock which it can reach or influence is cooled down to the winter temperature. In spring the current 
will be reversed ; it must still he of the temperature of the rock through which it passes, and will thus 
reproduce in summer the cold which had been stored up in winter, till the rock attains the summer tem- 
perature and the action is intermitted. Some cold must be lost, as I have hinted, by the transmission 
of central heat, but still a very small mass of rock will supply an immense mass of cool air. I do not 
know whether the specific heat of gypsum has been ascertained ; but suppose it the same as of lime, and 
every cubic foot of it in the hill will cool 150 cubic feet of air to the same degree. Assume the hill to 
be a pyramid whose base is a quarter of a mile and 150 feet high, this would supply eighty-five feet every 
second for six months, which seems more than sufficient. But secondly, this hill may communicate 
with extensive caverns or fissures full of air, extended horizontally, and within the reach of the trans- 
mitted influence of winter and summer. In the former they and the air they contain will be cooled ; 
but when the influence of the latter reaches them, it will expand the air, and this escaping by the cave 
will add its cooling powers. Such seems to be the case in some of the Italian caves, but I think the sup- 
position scarcely required at Illetzkaya. As to the degree of refrigeration, it obviously depends on the 
winter temperature ; but I would expect it to be increased by the evaporation. The materials of the hill, 
saliferous gypsum, must dry the included air completely, as their affinity for water is considerable ; on 
the other hand, after a spring thaw, we must expect to find the earth of the cave which is near the 
surface saturated with moisture ; and it is easily shown that arid air, even at or below 32°, will be 
1 Astronomer of Armagh, and Member of the Royal Irish Academy. 
2 c 2 
