226 ANSWERS TO PRACTICAL QUESTIONS 



67. Is a dusty boot hotter to the foot than a polished one ? 



(See Physics^ p. 194.) 



68. The top of a mountain is nearer the sun ; why is it 

 not warmer ? 



(See Question 62.) 



72. Can we find frost on the windows and on the stone- 

 flagging the same morning ? 



It requires a much intenser cold to produce the former 

 effect than the latter, as glass is a poorer conductor of 

 heat than stone. We frequently find frost on the flagging 

 early in the fall, but frost on the window is a sign of very 

 severe winter weather. 



73. Why will not snow "pack" into 'balls except in mild 

 weather ? 



The snow must be very near the melting-point for the 

 pressure of the hand to be sufficient to melt enough of 

 it to produce the phenomena of regelation. (Physics, 

 p. 202, ist note; also Tait's Recent Advances in Physical 

 Science, p. 129, and TyndalFs Forms of Water, p. 163.) 

 This principle involves the theory of Glaciers. "The 

 masses of snow cannot rest on the steep slopes of 

 Alpine summits. The pressure upon the under layers is 

 too great to allow them to remain upon their sloping 

 beds, and they are forced to descend. This descent is 

 accomplished in two forms-: that of an avalanche, one of 

 the most awful and imposing spectacles to witness ; or of 

 a glacier, which is really an avalanche of ice of extremely 

 slow motion. But the glacier differs from the ordinary 

 avalanche not only in that its motion is so slow, but in 

 that it consists of ice, thick, firm, and hard. The prin- 

 ciples involved in this transition of the loose, flaky 



