138 Professor Forbes's Thirteenth Letter on Glaciers. 



of a given point, at the same season, in different years. I 

 have obtained several such results on the Mer de Glace of 

 Chamouni, all of which tend to shew a marked increase of 

 the rates of motion during the two years which have elapsed 

 since my last measures were made. 



Thus, at station C, the Pierre Platte, opposite to the pro- 

 montory of Tacul,* from the 19th August 1844, to 21st July 

 1846 (701 days), the advance was 622 feet, or 1065 inches 

 daily. 



The following little Table shews the relation of this to 

 former years. 



The mean velocity was, therefore, about a fourth part 

 greater in 1845-6 than in 1843-4. 



The following Table shews the daily motion, in inches, of 

 a series of transverse stations nearly opposite to the Mon- 

 tanvert, and marked with the numbers D 2, D 5, D 6, D 3, 

 since the commencement of my observations. "f The first in 

 order was about 100 yards from the western shore, D 5 was 

 130 yards farther, D 6 was 75 yards farther, and on the axis 

 of the " dirt-bands :" D 3 was 60 yards farther, near the me- 

 dial moraine, and about 350 yards from the eastern side of 

 the glacier. 



Mean Daily Motions, 



* See Travels in the Alps, 2d Edit., p. 92 and 135, and Map annexed. 



t Travels, 2d ed., pp. 137-140. 



X From 25th July to 3d August only. 



