The Theory of Glacier motion. Sy 



crawling theory is founded c n the hypothesis of the varia- 

 tion in temperature of the interior of glacier ice, and until 

 that hypothesis is verified experimentally the theory cannot 

 be translated from the region of speculation into that of 

 reality. To Mr. Moseley's statement, that ice if opaque to 

 non-luminous is transparent to luminous heat, he urges that 

 this cannot apply to those portions of a glacier above the 

 snow line, nor to those portions of it below that line which 

 belong to the region of neve which share in the movement 

 of the general mass. Even in the region of the glacier, 

 when the substance is actual ice itself, it is doubtful if the 

 sun's heat penetrates many inches. The surface bears a 

 great resemblance to the upturned edges of a pack of slates, 

 and it becomes very opaque as it disintegrates with the 

 sun's heat. Nor would the sun's rays reach those portions 

 of a glacier covered with moraine and rubbish. In such parts, 

 therefore, the motion ought to be greatly diminished or to 

 be entirely arrested. If ice dilates with heat like lead, there 

 must be a point above which it does not expand, and where 

 its own motion will be nil. Above this point, if it is below 

 the summit level, the glacier will move uphill or be crushed 

 in its attempt to do so, and below it, each point will move 

 with a velocity proportional to its distance from the point 

 at rest, which is contrary to all experience" {Alpine J otcrrial^ 

 1870, 421). 



Mr. J. JBall, in the Philosophical Magazine for July, 1870, 

 urges that a glacier cannot move en masse by expansion 

 and contraction, since it is not a solid mass, but cut up into 

 sections by crevasses much deeper than the depths affected 

 by external changes of temperature. Again, all the experi- 

 ments (notably those of Agassiz) point to the interior of a 

 glacier having a more or less constant temperature, and not 

 being subject to great variations ; its surface beingcoated with 

 a nearly opaque crust, protects its interior from any but 

 trifling influences of luminous heat. The winter cold does not 



