observed on Glaciers. 19 



ice on the parts undefended by the stone. In the day time these 

 experience the direct radiation of the sun, and therefore melt 

 and run off in water. At night, it is true, the remaining sur- 

 face cools by radiation ; but this cold is propagated down- 

 wards, and on the return of day the superficial lamina is ne- 

 cessarily put in equilibrium with the air and melted by the 

 sun, and however cold the interior of the mass may be, the 

 surface will still be kept all day in a state of fusion. Thus 

 the degradation of the general surface of the ice will be in 

 proportion to the direct intensity of the sun's rays and the 

 time they shine ; while that of the surface beneath the stone 

 will only be in proportion to the excess of the mean tempera- 

 ture of day and night above 32°, diminished by the effect of 

 the thickness of the stone. This, of course, will produce a 

 difference of level, and a relative elevation of the stone sunk 

 as really observed. One curious, and at first sight, para- 

 doxical consequence seems to follow from this reasoning, viz., 

 that the ice of a glacier, or other great accumulation of the 

 kind, may, at some depth beneath the surface, have a per- 

 manent temperature very much below freezing, though in a 

 situation whose mean annual temperature is sensibly above 

 that point. In fact (continually to use the metaphorical ex- 

 pression already employed), there is no reason why waves of 

 cold, of any intensity below 32°, may not be propagated down- 

 wards into the interior of the ice ; but waves of heat above 

 that point, of com-se, never can. Thus, the cold of winter 

 and the frost produced by radiation in the clear nights of sum- 

 mer, will enter the mass and lower its internal temperature ; 

 while the heat of the summer air, and that imparted by solar 

 radiation, will mainly be employed in melting the surface, and 

 will rim off with the water produced. 



I am not aware of any observations on the internal tempe- 

 rature of glaciers ; they are of course difficult from their usual 

 rifty state ; but the point may not be unworthy the attention 

 of the scientific traveller. May not this be the cause of those 

 natural formations of ice which have been observed in caverns 

 in Teneriffe, and on some elevated points of the Jura chain, 

 below the level of perpetual snow ? It is obviously no matter 

 whether the interior mass in the above reasoning be ice or 



