15 



mouni whose position was ascertained by me in 1842. Its daily 

 motion was watched by me during that summer, and its annual 

 motion was ascertained by renewed observations in 1843, 1844, 

 1846, and again this year. I measured the distance along the ice 

 from the original position of the * Pierre platte' on the 27th June 

 1842 (ascertained by reference to fixed marks on the rocks) to its 

 position on the 12th July 1850, and found it to be 2520 feet. But, 

 of this distance, 1212 feet had been travelled at my previous obser- 

 vation on the 21st July 1846, leaving 1308 feet during the last 

 four years against 1212 in the first four. When more accurately 

 stated and compared, the mean annual and daily motions will stand 

 as follows : — 



We cannot infer, with absolute certainty, that the slight increase of 

 velocity here noticed since 1844 is due to a change in the conditions 

 of the glacier (although I believe that the recurrence of several snowy 

 seasons and the very marked increase of the volume and extent of 

 the glacier during these years would produce such an effect), because 

 it has moved nearly half-a-mile from its position when first observed, 

 and the part of the glacier on which it now lies may be subject to 

 different accelerating and retarding causes. 



" It is mentioned in my Thirteenth Letter on Glaciers in Profes- 

 sor Jameson's Journal, that T marked a fine solitary block towards 

 the centre of the Mer de Glace opposite ' Les Ponts' with the letter 

 V in 1846, and that I took angles for fixing its place with reference 

 to the adjacent rocks. It was then about 760 feet distant from the 

 west bank. I had little difficulty in recognizing the block in 1850, 

 although it had travelled a great distance, and was considerably lower 

 than the Montauvert. It had preserved its parallelism to the shore, 

 for I found it at almost the same distance from the west bank as at 

 first ; and by measuring carefully along the side of the glacier, I 

 estimated its progress in four years, from 30th July 1846 to 13th 

 July 1850, at 3255 feet. This gives, for the mean motion in 365 

 days, 822*8 feet, or the mean daily motion 27'05 inches, which is 

 remarkably large. Its position is very near the point of one of the 



