Natural History. 209 



and the walls at bottom were so evidently giving way, that I was 

 compelled, with extreme expense and inconvenience, to pull down the 

 whole inner walls and build them afresh, in a more secure manner. 

 From the same cause a new magazine, which government directed to 

 be built with an arched roof of brick-work, was, when complete, found 

 so very unsafe, that it was necessary to demolish it entirely and 

 rebuild it on a new plan, with a roof of tiles*. 



15. PROGRESSIVE MOTION OF THE GLACIERS. 



The ladder which M. de Saussure used in crossing the crevices in the 

 ice during his first visit to the Col du Geant, and which he left on the 

 upper part of the glacier, has lately been discovered imbedded in the 

 Mer de Glace, in a situation nearly opposite to the aiguille called 

 le Moine. This ladder, moving on with the body of ice, will thus 

 appear to have advanced three leagues since the year 1787. 



Captain Sherwill, in his relation of his ascent of Mont Blanc, 

 speaking of the glaciers, says, 4 In traversing these stagnated 

 oceans, very large blocks of granite, of many tons weight, may be 

 seen riding on the surface of the ice. These blocks have afforded 

 the means of ascertaining a fact of importance. The experiment I 

 am about to relate to you was made last year by some of the guides 

 of Chamouni. Two poles were erected, one on each side of the 

 glacier, out of reach of its movement, and so placed as to be in a 

 direct line with a block of granite. In the course of twelve months, 

 this block had entirely changed its position, as respecting the two 

 poles, and had advanced about one hundred yards on its march 

 towards the valley, a clear proof that the glaciers do move on, and 

 are continually diminishing at their lower extremity, by the melting 

 of the ice, and increasing at the upper end by the constant snows.' 



If the progress made by the ladder of M. de Saussure taken for 

 one year, and the result of the experiment made at the instigation of 

 Captain Sherwill, should not appear to agree, it must be recollected 

 that from the Col du Gant to the spot where the ladder is, is a 

 very rapid descent, and of course the march of the glacier would be 

 rapid in proportion ; whereas the experiment of Captain Sherwill 

 was made on a level part of the same glacier, the Mer de Glace, 

 where the ice is of a more compact texture than that at an elevation 

 of above ten thousand feet, and consequently its progress towards 

 its final issue would be somewhat slower t. 



16. ON THE COMPARATIVE QUANTITY OF SALT CONTAINED IN THE 

 WATERS OF THE OCEAN. (By M. E. Lenz.) 



The following experiments were made on the expedition of Captain 

 Kotzebue : Those with water at seven different places of the ocean, 

 and at various depths, tended to prove, that from the equator to 



* Calcutta Transactions. t Philosophical Magazine, N. S. ix. 32. 



VOL. II. AUG. 1831. P 



