406 



Prof. Tyndall on Ice and Glaciers. 



the crevasses of a glacier are the necessary consequences of its 

 motion." 



I have quite recently had a mould constructed for me by Mr. 

 Becker*, and yesterday (November 16th) made with it an expe- 

 riment which, on account of the ease with which it may be 

 performed, will interest all those who care about exhibiting 

 in a striking and instructive manner the effects of regelation. 

 The mould is shown in fig. 7. It consists of two pieces of 



cast iron, ABC and D F G, slightly wedge-shaped and held 

 together by the iron rectangle RE which is slipped over 

 them. The inner face of ABC is shown in fig. 8. In it is 

 hollowed out a semi-ring M N, with a semicylindrical passage 

 O leading into it. The inner face of D F G is similarly hollowed 

 out, so that when both faces are placed together, as in fig. 7, 

 they enclose a ring 4 inches in external diameter, from M to N, 

 and | of an inch in thickness, with the passage 0, 1 inch in 

 diameter, into which fits the polished iron plug P leading into 

 it. At q and r, fig. 8, are little pins which, fitting into holes 

 corresponding to them, keep the slabs ABC and D F G from 

 sliding over each other. 



The mould being first cooled by placing it for a short time in 

 a mixture of ice and water, fragments of ice are stuffed into the 



* I am continually indebted to this able mechanician for prompt and in- 

 telligent aid in the carrying out of my ideas. 



