96 Rev. C. Trotter. Physical Properties of Ice [Jan. 29, 



place exclusively by shearing, the direction as well as the extent of 

 the shear will vary from point to point, and a simple observation of 

 the flexure of the beam will not give a direct measure of the shearing 

 strength of ice at any point. Moreover, the experiments were all 

 made either during frosty weather, when the temperature of the ice 

 experimented upon was variable, and the conditions therefore very 

 different from those which obtain in the interior of a glacier, or else 

 in a warm atmosphere while the ice was thawing rapidly, and the 

 experiments could not be carried on for any considerable time under 

 unchanged conditions. 



III. New Experiments. 



Under these circumstances it seemed desirable that fresh direct 

 experiments on the shearing strength of ice should be made under 

 conditions differing as little as might be from those under which ice 

 actually shears in the interior of a glacier, and it occurred to me that 

 such experiments might be advantageously made in one of the arti- 

 ficial grottoes which are now excavated year after year for the benefit 

 of tourists in several of the more accessible Swiss glaciers. It seemed 

 that it would be possible in this way to carry out experiments upon 

 glacier ice at a nearly uniform temperature of about 0° C, and under 

 conditions as nearly resembling the interior of a glacier as we can 

 hope to attain to in experiments on hand specimens of ice. 



I accordingly spent part of the long vacation of 1883 at Grindel- 

 wald, and made a series of experiments in the grotto on the right 

 bank of the lower glacier, in order to see whether I could obtain 

 direct evidence of shearing under the influence of forces comparable 

 with those which Canon Moseley admits to be capable of being pro- 

 duced by the action of gravity in a moving glacier. 



Situation of the Experimental Grotto. 



The entrance to this year's grotto was at the base of a cliff of ice 

 which I estimated at about 25 metres high. It was, by a rough 

 barometrical comparison with Grrindelwald, about 1275 metres above 

 the sea-level, and about 75 metres above and perhaps 300 metres 

 distant from the place where the glacier, now reduced at this point to 

 a comparatively narrow tongue of ice, plunges into a deep and narrow 

 gorge. 



At the time of my arrival in Grindelwald (June 27) the grotto, the 

 floor of which sloped slightly upwards, penetrated for about 18 metres 

 nearly in a straight line, making an angle of about 55° with the face 

 of the ice cliff, and then for about 8*5 metres further in a direction 

 making an angle of about 3° only with the face of the cliff. It was a 

 gallery nearly 2 metres high, and rather more than a metre wide. 



