Variation of Motion at different Seasons. 331 



From these conflicting results, it is plain that there have 

 been reckless assertions made, and also observations un- 

 worthy of confidence. It is very much to be desired for the 

 credit of all the parties who have had a share in the expe- 

 riments on the glacier of the Aar, that the source of these 

 discordances should be investigated. I remain, my dear Sir, 



yours very truly, 



James D. Forbes. 



To Professor Jameson. 



Observations on the Motion of the Glaciers of Chamouni at 

 different seasons, 



I am now enabled to present a view of the actual progress of two 

 glaciers during every part of the year from direct observation. For 

 these I am indebted to the intelligent and persevering zeal of my 

 excellent guide and assistant at Chamouni, Auguste Balmat, of 

 whose character I have had the pleasure of forming a more and 

 more favourable estimate the longer I have been acquainted with 

 him. To the long training of the laborious summer of 1842, when 

 he assisted me, he adds the further experience derived from my visits 

 in 1843 and 1844, in the latter of which especially he became fami- 

 liar with the nice precautions requisite in conducting the most accu- 

 rate measurements, and received instructions from me which ren- 

 dered him perfectly competent to continue by himself the simpler 

 kind of measurements which I have alone required of him. The 

 extraordinary exertions which he used to obtain the winter motion 

 of the block D 7, under the Montanvert, in 1842—43, have been 

 noticed in my former publications. On one or two occasions, as I 

 learned afterwards from himself, being unable to ascend the usual 

 path to the Montanvert for fear of spring avalanches, he actually 

 clambered with a companion up the rugged ascent from the source 

 of the Arveiron, plunging continually up to the middle in snow, for 

 no other purpose than to make the observation which I had requested 

 of him ; and it would be unjust not to mention at the same time the 

 admirable, because rare, generosity, with which he positively refused 

 for himself any share of the remuneration which I pressed upon him 

 the following summer, as some recompense for the fatigues and dan- 

 gers which he had braved to obtain for me this information. With 

 such a person, my confidence in the observations which he has made 

 at points much more accessible, and with the experience of some 

 additional years, is complete. I do not mean that mistakes may 

 not occur, or even that the measures may not be less exact than I 

 might have taken myself; but from my knowledge of the man, I am 

 nearly as confident in their being faithfully reported^ exactly as 

 they were made, as if I had done so myself. 



With a view to lighten the labour as much as possible, I selected 



