5^ Fatal Accident which happened to 



clouds during the fix hours I remained on it. I was ex- 

 ceedingly cold, and, in order to warm ourfelves, 1 and my 

 guides were obliged to conftruct a hut on the ridge of 

 rocks neareft the fummit. We had at hand large pieces of 

 flate, and our building was lo folic! that it ftill exifts, and 

 has (heltered more than one curious traveller from the fe- 

 verity of the weather. 



The glacier, which covers this fummit, differs from the 

 greater part of thofe accumulations of ice known under that 

 name in this reipect, that the latter generally occupy the 

 valleys, or the defijes in which the ice has not been ori- 

 ginally formed, but to which it has funk down by its own 

 weight, and the preffure of the ice above it; whereas the ice 

 of Buet has been formed in the place where it exifts; and 

 at that height in our parallel the fnow never melts in 

 fu miner. This mountain, therefore, may ferve to determine 

 with fome precision the lowed boundary of the fnow in our 

 climates. 



Thus, for example, by obfcrving from Geneva, through a 

 telefcope furnifhed with a micrometer, the vertical angle 

 comprehended between the fummit of the glacier and the 

 loweft boundary of the fnow, I found it to be 16' 14", which, 

 taking the diltanceof Buet from Geneva at 29820 toifes, cor- 

 refpondsto 141 toifes, the diftanceof this boundary below the 

 fummit, which places it at 1453 toifes above the level of the lea. 



It may here be afked, what is the mean annual tempera- 

 ture at this height in our latitude ? We have pointed out 

 fomewhere in our Journal a very fimple formula, which 

 Sauffure deduced from a great number of obfervations, and 

 which reprefents very well the law of the decrement of the 

 mean heat of the atmofphere from the bottom upwards. This 

 decrement is a hundredth part of a degree of the thermometer 

 of Reaumur per toile of perpendicular elevation. This for- 



rills, when compared with the valleys tilled with ice, from which they flowed. 

 Mont Blanc, which rofe above theft- valleys, fecmed capable of fumilhing 

 alone, for a long time, a fufficiency of water for a river, fo much was 

 it loaded with ice from the top to the bottom ; that is to fay throughout 

 a prodigious extent — Recberebes fur les Modif cations de VAtmofpbere, 

 vol. ii. p. 390. 



mul a, 



