1885.] 



and on the Motion of Glaciers. 



97 



I had a lateral gallery excavated to contain my apparatus at the 

 extremity of the main gallery, and on the side opposite to the edge 

 of the glacier. This was of the same height as the main gallery, 

 and about 3 metres long. The entrance was of the same width as 

 the main gallery, but the end was somewhat wider, perhaps 1'7 metre. 

 This lateral gallery was shut off by a rough door of planks from the 

 main gallery, which was afterwards extended for a few metres beyond 

 the entrance to the side gallery. The place in which my experiments 

 were conducted was therefore some 18 metres from the edge of the 

 glacier, 25 or 30 metres below its upper surface, and probably at 

 least an equal distance above its bed. 



There were some longitudinal crevasses of considerable size on the 

 lower part of the glacier, and it is probable that one of these was not 

 very far from the experimental gallery. I infer this from the fact 

 that there was perceptibly more light in the side gallery than in the 

 main gallery at the point where the side gallery branched off from it, 

 and the light increased sensibly during the time (rather more than 

 five weeks) that my experiments lasted. I attribute this increase of 

 light to the melting of the side of a crevasse, and am disposed to 

 estimate the distance from the end of the experimental gallery to the 

 nearest crevasse at from 5 to 10 metres. After the first few days T 

 kept maximum and minimum thermometers on the wooden frame 

 which supported my apparatus. The extreme readings were 0° C. 

 and 2° C. The temperature of the air and the gallery must have 

 been raised from time to time by the presence of myself and others, 

 particularly when a light was used, but for the greater part of the 

 time the temperature of the air can scarcely have differed sensibly 

 from 0° C. 



The pieces of ice used in my first experiments were part of the 

 material excavated from the side gallery. In the last I used a 

 block hewn out expressly from the interior of the glacier. I always 

 chose the most solid and transparent, and therefore presumably the 

 hardest and strongest, pieces I could find. The blocks hewn by the 

 pick were cut roughly to the required size and shape with a coarse- 

 toothed saw ; they were finished with a carpenter's plane set so as to 

 cut a rather coarse shaving. 



The apparatus used was in principle the same as Canon Moseley's. 

 My apparatus was, however, disposed symmetrically so as to produce 

 a shear in two parallel planes simultaneously. I was thus enabled to 

 simplify the arrangements for fixing the apparatus, and to make my 

 measurements more easily and accurately. Each of three pieces of 

 board, AB (fig. 1), had a square notch cut in one side, so that when 

 the short bar, CD, was fixed in its place by two screws, the whole 

 formed a block with a square hole in its centre. A hook by which the 



VOL. xxxviii. , H 



