148 



THE GEOLOGIST. 



burgh ; and he states, that if anything similar occurs at 

 Orenburg, he sees no difficulty in explaining the phenomena 

 of the ice cave. Rejecting diurnal fluctuations, and consi- 

 dering the summer heat as a single wave propagated down- 

 wards, alternately with a single winter wave of cold, every 

 point in the interior of an insulated hill, rising above the 

 level plain, will be invaded by these waves in succession, con- 

 verging towards the centre in the form of shells, similar to the 

 external surface at times, which will deviate farther from 

 midwinter and midsummer the deeper the point is in the 

 interior ; so that, at certain depths, the cold wave will arrive 

 in midsummer, and the heat wave in midwinter. A cave, if 

 not very wide-mouthed and airy, penetrating to such a point, 

 will have its temperature determined by that of the solid rock 

 which forms its walls, and will be so alternately heated and 

 cooled. The analogy of waves, adds Sir John Herschel, is 

 not strictly that of the progress of heat in solids, but nearly 

 enough so for the purposes of the argument. 

 - 2. — On some phenomena observed on Glaciers, and on the 

 internal temperature of large masses of ice or snoiv ; ivith some 

 remarks on the natural ice caves which occur below the limits 

 of perpetual snow. By Sir John Herschel, Bart, — (Written in 

 1829.) 



The glacial phenomena first described are the blocks of 

 granite which rest on pedestals of ice of less diameter than 

 the blocks, and rising above the general surface of the 

 glacier ; and the occurrence of smaller fragments sunk into 

 the ice, the depth of the hollow being, within certain limits, 

 increased proportion ably to the smallness of the fragments. 

 In both cases the heating and cooling influences are consi- 

 dered to be equal. These apparently opposite phenomena 

 afi'ord. Sir John Herschel says, a very pretty illustration of 

 the laws of the propagation of heat through bad conductors, 

 and the steps by which an average temperature is attained in 



