Review of the Controversy Regarding tJie Motion of Glaciers. 149 



Mr, Croll has very satisfactorily shown from Canon Moseley's own 

 data, that the theory of expansion fails to give the motion required 

 in summer, by observation. He says: 



'• It i.s a necessary condition of "Mr. Moseley's theory that the heat 

 should pass easily into and out of a glacier, for unless this were the 

 case, sudden changes of temperature could produce little or no effect 

 on the great mass of the glacier. How, then, is it possible that during 

 the heat of summer the temperature of the glacier could vary much? 

 During that season, in the lower valleys at least, everything, with the 

 exception of the glacier, is above the freezing point; consequently, 

 when the glacier goes into the shade, there is nothing to lower the ice 

 below^ the freezing point, and as the sun's rays do not raise the tem- 

 perature of the ice above the freezing point, the temperature of the 

 glacier must (therefore) remain unaltered during that season. It 

 follows, therefore, that instead of moving more rapidly during the 

 middle of summer than during the middle of winter, the glacier 

 should, according to Moseley's theory, have no motion whatever dur- 

 ing summer. ^5^ 



But is not the same condition equally necessary for Mr. CroU's 

 theory, viz.: the ready transmission of heat into the mass of a glacier, 

 in whatever form that heat may pass ? We have already shown that 

 the low conductivity of ice excludes this condition, and, consequently, 

 invalidates the theory. Granting, what is probably true, that during 

 the summer a small amount of heat penetrates to a slight depth the 

 glacial mass, the approach of night, or winter, reverses the case, and 

 then, instead of absorbing, the ice gives out the heat it had already 

 taken in, and its superficial temperature falls below the freezing point. 

 In these cirumstances no conduction of heat into the interior is possi- 

 ble, and radiation from without, if it were appealed to for aid, is ex- 

 cluded by the layer of snoAV which covers the ice. "The appearance 

 of the glaciers in winter is very impressive — all sounds are stilled j 

 the cascades, which in summer fill the air with their music, are silent, 

 hanging from the ledge of the rocks in fluted columns of ice." " There 

 is no danger in entering the vault of the arveiron, for the ice seems as 

 firm as marble."! Consequently, if, on Canon Mosele/s theory, no 

 motion can ensue during the summer, on account of the variability of 

 the temperature of the ice, on ISIr. CroU's theory, no motion can ensue 

 during winter, because everything around the glacier, and its own 



=:■• L. E. & D., Phil. Mag., September, 1870. 

 t Tyndall's Fonns of Water, pp. 89-92. 



