122 



On the Apparent Viscosity of Ice. 



Wire. 



Time, in minutes. 



Conductivity. 



Silver 



13| 

 15i 



100 

 73-6 







The difference is here one eighth of the whole time, and is 

 again in favour of the silver wire. 



These results prove that the time increases as the conduc- 

 tivity decreases ; but we have been unable to find any simple 

 relation connecting them together. 



Another experiment was made to determine the influence 

 of the weight used. Three pieces of iron wire, cut from the 

 same sample, were loaded with different weights and placed 

 across a block of ice. The times taken in cutting through 

 were as follows: — 



Load. 



Time, in minutes. 



Load X Time. 



51b. 



7| lb. 



12| lb. 



225 

 146| 



84 



1125 

 1099 

 1090 



The numbers in the third column show that the time taken 

 is approximately inversely proportional to the load. 



Amongst the experiments made by Pfaff* to prove the 

 plasticity of ice is the following one : — An iron tube placed 

 upright on a block of ice is completely surrounded with snow 

 to prevent its temperature rising above 0° C, and a pressure 

 of about two atmospheres is applied at its upper end by means 

 of a one-armed lever : the tube slowly forced its way into the 

 ice, and after an hour had sunk 3 centim. At the close of the 

 experiment Pfaff found inside the iron tube a cylinder of ice, 

 which fitted so closely that it would not fall out by its own 

 weight. From this Pfaff concludes that the sinking of the 

 iron tube is due almost entirely to the plasticity of ice, and 

 only minutely, if at all, to the effect of pressure in lowering 

 the freezing-point of water. 



It is, however, at once evident that the explanation given 

 of Bottomley's experiment also applies to this; the only differ- 

 ence being that, whereas in the former case the heat necessary 

 for the liquefaction of the ice under presure is obtained from 



* Pogg. Ann. civ. p. 169 (1875). 



