126 VISCOUS THEORY OF GLACIER MOTION. [1846. 



the further experience derived from my visits in 1843 and 1844, 

 in the latter of which especially he became familiar with the 

 nice precautions requisite in conducting the most accurate mea- 

 surements, and received instructions from me which rendered 

 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 1842-3, have been 

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

 as 1 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 obser- 

 vation 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 fol- 

 lowing summer, as some recompense for the fatigues and 

 dangers which he had braved to obtain for me this information. 

 With such a person, my confidence in the observations which 

 he has since 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 two stations on the Glacier of Bossons, and desired 

 Balmat to select two on the Glacier des Bois (the outlet of the 

 Mer de Glace towards the valley of Chamouni) ; all these points 

 being tolerably accessible at every season of the year. 



The general method of observation was the following : 

 vertical holes were driven into the ice with a 4-foot blasting 

 iron, at the points whose motion was to be determined ; and 



