168 G. F. Becker—Temperature and Glaciation. 
The formation of glaciers must be confined, under otherwise 
equal conditions, to areas lying between certain isotherms. If 
a mountain is supposed to rise in a tropical country to an 
indefinite height, a temperature will prevail at its foot too high 
to allow of the formation of ice, and its peak may be supposed 
to stand at an elevation where the cold is too great to permit of 
any considerable precipitation. Dr. Tyndall has drawn atten- 
tion to this fact and pointed out that, were the mountains high 
enough, there would be an upper as well as a lower snow line. 
this basin takes place in the form of the glacial stream, which 
descends to a lower level until a temperature is reached at 
and evaporation reéstablish the equilibrium between dissipa- 
tion and solid precipitation. As observations show that both 
* According to Sir W. Thomson’s experiments, and Prof. Clausius’s computations 
(Clausius’ Mech. Warmetheorie, i, 172), a pressure of one atmosphere depresses 
the melting point of ice 0:00733°C. It follows that a pressure of about a ton per 
square inch, or many thousarid feet of snow, would be required to reduce the 
temperature of fusion 1°. 
