Mr. R. D. Oldham on the Modulus of Cohesion of Ice. 241 



pressure less than this could produce any change of shape in 

 the ice (for I feel sure that, if continuous for an indefinite 

 period, a pressure far less than this would be sufficient to pro- 

 duce an indefinite change of form), but because, from the 

 nature of the case, any such slow and gradual yielding could 

 not be detected, both on account of the warmth of the testing- 

 room and the small range of motion allowed by the machine, 

 while the pressure at which the ice began to yield by the con- 

 tinuous formation of small cracks could be comparatively 

 easily determined with sufficient approach to accuracy. 



As the pressure was increased the yielding went on faster 

 and faster, till when a pressure of about 400 Jb. on the square 

 inch was reached the ice could no longer yield in this conti- 

 nuous manner, but was crushed to pieces. The pressure at 

 this point is noted in the fourth and fifth columns of the 

 Table below: — 



Pressures. 





For commencement of 

 yielding. 



For crushing. 





Pounds per 

 square inch. 



Modulus, 

 in feet. 



Pounds per 

 square inch. 



Modulus, 

 in feet. 



1. 



2. 

 3. 



. -4. 

 5. 

 6. 



7. 

 8. 





297 



376 

 403 

 376 

 403 



354-5 

 457-8 

 369 



457-8 



357-8 

 357-8 



869 



1122 



904 



1122 



877 



877 



V Not crushed. 







121-5 

 1534 

 164-5 

 153-4 

 164-5 



Average .. 



151-5 



371 



392-4 



960 



The above Table shows that, under a pressure of a column 

 of its own substance 370 feet in height, ice must yield, and 

 that no slow pressure greater than one equivalent to that depth 

 of ice could be transmitted by ice, while under a pressure of 

 960 feet of its own substance ice would be crushed; but, to 

 prevent any error on the wrong side, I shall take the modulus 

 of ice at 1000 feet, or nearly three times what was actually 

 observed. 



In order to apply these figures to the investigation of how 

 far it would be possible for a glacier to scoop out a lake-basin 

 of any considerable size, it will be necessary to form some idea 

 of what is the friction between the base of a glacier and its 

 bed. Now on this point we have, fortunately, experimental 

 evidence ; for the angle of repose of clean ice on moderately 



Phil. Mag. S. 5. Vol. 7. No. 43. April 1879. U 



