SIXTEENTH LETTER ON GLACIERS. [1850. 



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 2 7 '05 inches, which is remarkably large. Its position 

 is very near the point of one of the " dirt-bands," but a little 

 nearer the western bank. It lies, however, on the band. 



I shall now give the sequel of my guide Auguste Balmat's 

 observations on the motion of the Glacier des Bois (the outlet 

 of the Mer de Glace), and of the Glacier des Bossons, since the 

 period to which the table in my Fourteenth Letter extends,* which 

 will be found to embrace continuous observations, by periods of 

 a few weeks from the 2d October 1844 to the 21st November 

 1845. They were continued in like manner until the 19th 

 February 1846, when they were interrupted by Balmat's illness, 

 which was accompanied by inflammation of the eyes. But in 

 October of the same year they were resumed, and were con- 

 tinued without intermission until the end of June 1848, em- 

 bracing altogether a period of nearly four years, with only eight 

 months' intermission. It is necessary to observe that the 

 station on the glacier of Bossons was altogether changed after 

 the above mentioned interruption, being transferred from the 

 west to the east side (in the same region of the glacier), and it 

 was 340 feet from the bank. The station on the Glacier des 

 Bois was almost unchanged [?], and was about 280 feet from the 

 north bank, between the Cote du Piget and the acclivity of the 

 Chapeau. I have added a column giving the mean of the tem- 

 peratures of the several periods of observation, carefully calcu- 

 lated from the published observations at Geneva and the great 

 St. Bernard, on the same principle as I have fully explained in 

 my Fourteenth Letter above referred to.f The comparisons of 

 the temperature and the rate of motion lead to conclusions 

 similar to those which I have drawn in that paper from the 

 earlier observations, the general observation always holding that 

 the acceleration in spring is in a greater proportion to the tem- 

 perature than at any other season of the year, on account of 



* [Borrowed from the paper ip the Philosophical Transactions, reprinted at 

 page 128 of this volume.] f [See rather p. 131 above.] 



