and Motion of Glaciers. 369 



wood, so that, when the protuberance and the cavity were con- 

 centric, a distance of a quarter of an inch separated the convex 

 Fiff. 3. 



surface of the former from the concave surface of the latter. 

 Fig. -i shows the arrangement in section. The pins of brass, ab, 

 fixed in the slab AB, and entering suitable apertures in the 

 mould CD, served to keep the two surfaces concentric. A lump 

 of clear ice was placed in the cavity, the protuberance was 

 brought down upon it, and the mould submitted to hydraulic 

 pressure. After a short interval it was taken from the press, and 

 when the upper slab was removed, a smooth concave surface of 

 ice was exposed. By tapping the conical plug ^j, this ice was 

 lifted from the cavity, the lump having been converted by pressure 

 into a hard transparent cup of ice. 



The application of the results here obtained to the " viscous 

 flow'' of glaciers will perhaps be facilitated by the following 

 additional experiments. 



A block of boxwood (A, fig. 5), 4 inches 

 long, 3 wide and 3 deep, had its upjier 

 surface slightly curved, and a longitudinal 

 groove (shown in dots in the figure), an 

 inch wide and an inch deep, worked into 

 it. A slab of the wood was prepared, the 

 under surface of which was that of a con- 

 vex cylinder, curved to the same degree as 

 the concave surface of the former piece. 

 The arrangement is shown in section at B. 

 A straight prism of clear ice, 4 inches in 

 length, an inch wide, and a little more 

 than an inch in depth, was ])laced in the 

 groove, and the upper slab of boxwood was 



placed upon it. The mould was submitted to hydraulic pressure,as 

 in the former cases; the jirism broke as a matter of course, but 



Fig. 5. 



