506 THE LIFE OF JAMES 1). FORBES. [CHAP. 



hearsay estimates by the guides. M. Kendu seems to 

 have been more aware of the importance of the determi- 

 nation of the rate of motion of glaciers than any other 

 author ; but the best information ^hich he could collect 

 in 1841 did not much tend to clear up his doubts. He 

 gives the following rates of motion of the Mer de 

 Glace, or Glacier des Bois, without being able to decide 

 upon which is the most trustworthy : 242 feet per annum ; 

 442 feet per annum ; a foot a day ; 400 feet per annum ; 

 and 40 feet per annum, or one-tenth of the last! a dif- 

 ference which he attributes to the different rates of 

 motion of the centre and sides. 1 De Charpentier, so far 

 as I recollect, offers no opinion in his work on glaciers 

 as to what is to be considered as their rate of motion. I 

 was not therefore wrong in supposing that the actual 

 progress of a glacier was yet a new problem, when I com- 

 menced my observations an the Mer de Glace in 1842.' 



* I had myself been witness to the position on the Gla- 

 cier of the Aar, in 1841, of the stone whose place had 

 been noted by Hugi fourteen years before, and it was 

 manifest that it had moved several thousand feet. In 

 conformity with the prevalent view of the motion of the 

 ice being perceptible chiefly in summer, I made the hypo- 

 thesis that the annual motion may be imagined to take 

 place wholly during four months of the year, with its 

 maximum intensity, and to stand still for the remainder. 

 With this rude guide, and supposing the annual motion 

 of some glaciers to approach 400 feet per annum (as a 

 moderate estimate from the previous data), we might 

 expect a motion of at least three feet per diem for a short 

 time in the height of summer. There appeared no reason 

 why a quantity ten times less should not be accurately 

 measured, and I, therefore, felt confident that the laws 

 of motion of the ice of any glacier in its various parts, 

 and at different seasons, might be determined from a 

 moderate number of daily observations/ 



1 1 went to Switzerland, therefore, fully prepared, and 

 not a little anxious to make an experiment which seemed 



1 Me moires, c. x. 95. 



