Motion of the Glacier of La Brenva. 97 



1818 in the bottom of the valley, from which it is now only 

 about 100 yards distant (see the Plan, Plate II., fig. 1), 

 whilst it is tearing or ploughing up the soil on the southern 

 bank, marked in Plate I., fig. 2, on the left hand side. 



The same gentleman, M. Guicharda, has himself made, 

 with considerable labour, observations intended to test the 

 reality of the movement of the glacier during winter, which 

 confirm, in every particular, those which I have already pub- 

 lished regarding the glaciers of Chamouni. The movement 

 appears to be very regular ; but, from the position selected 

 for the measurement (the terminal face of the glacier), where 

 the friction is most intense, and the movement slow (see 

 Eleventh Letter), and where the danger from falling stones 

 is such as absolutely to prevent the continuance of observa- 

 tions during summer, they are less comparable and complete 

 than would otherwise have been the case. Having explain- 

 ed fully to MM. Carrel and Guicharda my methods of ob- 

 serving, and pointed out a more convenient site, we may 

 hope that we shall have a continuous series of trustworthy 

 observations of this most interesting glacier. In the mean- 

 time I publish, with M. Carrel's permission, the degree of 

 motion of a stake fixed in the ice, near the lowest extremity 

 of the glacier, and little elevated above the soil. 



Mar. 21, 1 to Apr. 2, 10 1-18 — 0-10 



The mean daily motion is about 5 English inches, and it 

 is probable, from the discrepancy of the 5th and 6th observa- 

 tions, that the measurement of the 30th January was faulty. 



VOL. XLIl. NO. LXXXIII. — JANUARY 1847. G 



