G. F. Becker—Temperature and Glaciation. 173 
greater extent than is possible in the deep gorges in the White 
Mountains, the Adirondacks and elsewhere, in which ice is 
‘nearly or quite permanent. Such occurrences make it clear 
that the direct heat of the sun is of the first importance in the 
dissipation of glacial ice or névé. 
certain amount of névé is not melted but evaporated. 
Indeed, according to Professor Whitney, the snow on the south- 
ern side of Mt. Shasta diminishes in volume almost exclusively 
from this cause, but a fixed amount of heat employed in dissipa- 
tion by evaporation must produce a far smaller effect in the 
reduction of accumulated névé, than if it were employed in 
merely melting the snow or ice, for evaporation can go on rap- 
idly only in dry air; and since the air is an extremely poor con- 
ductor, and has a low specific heat, most of the latent heat ab- 
sorbed in volatilization of the water must be withdrawn from 
the underlying snow, and will thus counteract the tendency to 
melting. Indeed, since it is said to be possible to freeze water 
by evaporation and radiation from its own surface under favor- 
able atmospheric conditions, at temperatures much above the 
reezing point, it is @ prior’ probable that in a very dry atmos- 
ing. The melting effect of rain is no doubt very considerable, 
though as a certain quantity of water appears to be essential to 
glaciers. The melting effect of rain upou snow can readily be 
calculated if the temperatures of the two substances are known. 
“Tf that of the rain is plus 5° and that of the snow minus 5°, 
the melting of a weight of snow equal to one sixteenth part of 
fact of greater precipitation probably involved more cloudy 
Weather or a shorter exposure of the ice to sunshine. 
* 
