[barnes] 



THE PHYSICAL CONSTANTS OF ICE 



17 



At this temperature, the viscosity of a glacier is about 12500 s lO^o^ or 

 some 6350 times as much. This, he thinks, may be due to the fact that 

 the optic axis of glacier grains are at all angles and lock each other. 



Hess showed that the admixture of sand and dust with ice increases 

 the viscosity; hence he concludes, that the plasticity of glacier ice near 

 the ground is less than for that higher up. Since the viscosity of ice 

 increases with the time for slow steady application of small loads, Hess 

 calculates from his experiments that the coefficient for long flowing 

 glacier ice must be of the order of a x lOi^ where a lies between 1 and 

 100. Hence he concludes that for long continued loads the viscosity of 

 ice compares with steel, while for short loads it compares with zinc, the 

 coefficient of viscosity for steel being 6 x lOis and that for zinc being 

 4 X 1011. 



TABLE VIII. 



Elasticity and Viscosity. 



Observer. 



Kind of Ice . 



Young's Modulus. 



Viscosity. 



Moseley.. . 

 Bevan . . . . 



Reusch 



Hess 



McConnell. 



McConnell . 



Hess 



Weinberg... 

 Deeley 



Clear ice 



Clear ice and glacier ice 



Ordinary ice 



92700 Kgs cm -2 



60000 



23632 



27600 



3 X IQio gm 



5000 



Glacier ice 



134 xllOio 



order of lO^o " 



1.24x1010 " 



1.25x1014 " 



Observations were made by Hess to determine the dependence of 

 the velocity of flow on the pressure. For this purpose an iron tube 25 

 cm. long and 6 cm. wide, with a conical orifice running down to 4.5 cm., 

 was arranged. Pure air-free water was frozen in the tube, and a piston 

 was fitted in one end to which a long arm, weighted with 87.5 kilo- 

 grams, was attached. During the experiment the tube was surrounded 

 with pure snow. The flow was found to increase very rapidly with in- 

 creased pressure, and it was found that, once the flow had started, a com- 

 paratively small pressure was sufficient to maintain it. 



Sec. III., 1909. 2. 



