the Descent of Glaciers by their Weight only. 143 



shearing-apparatus when the temperature was above freezing, 

 and loaded it with the weights specified in the first column of the 

 following Table. It sheared through the distances specified in 

 the second column in the times given in the third. 



Load, in pounds. 



Distance sheared, 

 in inches. 



Time, in minutes. 



23 

 121 



208 

 208 



208 

 208 



208 



1 







3 



8 



h 



5 



8 



i 

 i 



5 

 5 

 25 

 30 

 40 

 45 

 55 



A second piece of ice, similar to the above, was placed in the 

 same apparatus at 6J o'clock in the evening of the same day and 

 loaded with 112J lbs., being at the rate of 63*6 lbs. per square 

 inch. At 8 o'clock in the evening the upper surface of the cy- 

 linder of ice was found to have yielded ^ inch. It was then 

 left thus loaded all night. At 10J next morning it was examined 

 again, and found not to have sheared at all during the night. 

 The night had been frosty, but the frost had not been severe. 



The unit of shear being given, the equality of the work through 

 a given distance of the resistances, to the work through the 

 same distance of the forces which cause the glacier to descend, 

 whatever they may be, is independent of the length of time. If 

 the resistances work slowly, the forces which overcome them 

 work also slowly and in the same ratio. The conclusion I have 

 drawn from this equality remains, therefore, unaffected by the 

 question of time. 



Mr. Matthews, however, and M. Heim after him, as well as 

 Mr. Ball, deny that glacier-ice shears at all. They say that it 

 bends. The following is Mr. Matthews's experiment as de- 

 scribed by himself : — 



" A plank of ice 6 inches wide and 2| inches in thickness was 

 sawn from the frozen surface of a pond, and supported at each 

 end by bearers exactly 6 feet apart. The whole weight of the 

 plank between the bearers could not have exceeded 37j lbs., and 

 its cross section was nowhere less than 14 square inches. Ac- 

 cording to the views of Canon Moseley, shearing must surely have 

 been impossible. Yet what was the result ? From the moment 

 the plank was placed in position it began to sink, and continued 

 to do so until it touched the surface over which it was sup- 



