GEOLOGY. 361 



accounts for the continuity of tlic mass of the glacier, without supposing, 

 with Professor Forbes, that ice is of a, viscous or plastic nature. 



Professor Tyndall has illustrated the lamina?, or clcavable nature of ice, 

 by many beautiful experiments. In one case, he succeeded in impressing, 

 upon a transparent prism of ice, a lamination which might be mistaken for 

 that of gypsum. 



By means of a small hydraulic press, he converts spheres of ice into flat 

 cakes and transparent lenses a straight prism of ice six inches long is 

 passed through a series of moulds augmenting in curvature, and finally 

 comes out bent into a semi-ring. A piece of ice is placed in a hemispherical 

 cavity, and is pressed upon by a proruberance not large enough to fill the 

 cavity, and is thus squeezed into a cup. In short, every observation made 

 upon glaciers, and adduced by writers upon the subject in proof of the plas- 

 ticity of ice, is shown to be capable of perfect imitation with hand specimens 

 in the laboratory. These experiments demonstrate a capacity on the part 

 of small masses of ice hitherto denied to them by writers upon this subject. 

 They prove to all appearance that the substance is even more plastic than it 

 has hitherto been supposed to be. 



ASCENT OF CHIMBORAZO. 



The summit of the Chimborazo has lately been found to be quite ascend- 

 able. When Baron Humboldt, with his friend Bonpland, on the 23d of 

 June, 1802, meant to ascend the Chimborazo, which at that time was con- 

 sidered to be the highest mountain on earth, he had to turn back at the 

 height of 5,909 metres, an insurmountable wall of rock barring his advance. 

 Boussingault, the second who attempted the ascent, arrived, on the 16th of 

 December, 1831, only up to 6,004 metres, ninety-five metres higher than 

 Humboldt. A late number of the Journal dcs Debats publishes a letter from 

 the French traveller, M. Jules Re'my, who, in company with an English 

 traveller, Mr. Brcnchlcy, ascended the mountain from a different side, on 

 the 3d of November, 1856; and, although wrapped in entirely by thick veils 

 of clouds, and forced by a violent storm to return, yet attained the height 

 of 6,543 metres (according to Humboldt's trigonometrical survey, the height 

 of the mountain is 6,544 metres), where the travellers lit a fire. It is ques- 

 tionable if M. Remy reached the absolute top of the mountain, but no doubt 

 is now left that this can be accomplished. The column of air at that height 

 was still quite sufficient for breathing. The shortness of breath and the 

 other symptoms usually noticed on reaching such heights have been per- 

 ceived neither by M. Remy nor by his English companion, rs the former ex- 

 pressly states. 



ON THE DENSITY AND MASS OF COMETS. 

 BY M. BABIXET. 



All astronomers are agreed that the mass and density of comets are very 

 small, and that their attraction cannot produce any sensible effect upon the 



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