146 . Mr. H, H. Howorth on 



evidence tends to shew that ice at or about 0°C. is just as truly 

 viscous as pitch or sealing wax at temperatures at which 

 they are brittle, but yet capable of yielding to the continuous 

 application of a very moderate force. The viscosity of ice> 

 however, probably diminishes very rapidly with the tem- 

 perature This is in complete accordance with the 



facts of the changes which take place in a glacier during the 

 winter. The terminal melting ceases, but the advance of 

 the end of the glacier into the valley is very slow, and 

 probably ceases altogether in the depth of winter. Higher 

 up, the forward movement of the surface continues, though 

 at a slower rate than in summer, and though the glacier 

 does not lengthen much in winter, it thickens considerably, 

 ;and the surface rises, often through many feet, so as to 

 make up the enormous waste of the summer." 



In May, 1887, Dr. Mann read an important paper before 

 the Royal Society upon some experiments he performed in 

 the Engadine upon the shearing of ice. In these experiments, 

 as he tells us, in order to eliminate the influence of regelation, 

 the experiments were carried on at low temperatures, the 

 highest being —2*6 C, number 2 — I'O^C, and number 3 

 — 0'5° C. The ice was frozen in a cylindrical mould, and 

 in order to exclude air the water was boiled. Without 

 giving the details the result obtained by Dr. Bain was that 

 " ice subjected to tension stretches continuously by amounts 

 which evidently depend on the temperature and on the 

 tension stress. When the stress is great, and the temperature 

 not very low, it amounted to as much as i per cent of the 

 whole length per day. When the temperature is lower and 

 the stress is less, the extension is less, but still such as can 

 be measured. So continuous and definite is the extension 



that it can even be measured from hour to hour 



Hence differential motions resulted in the ice. These motions 

 and extensions took place at temperatures which preclude 



