

xv.] FORBES 1 GLACIER DISCOVERIES. 505 



advance at the rate of fourteen feet a year, and those of 

 Grindelwald twenty-five feet a year : whereas, as we 

 shall see, such spaces are actually traversed by most 

 glaciers in the course of a few days. This statement is 

 quoted by Captain Hall l and other recent writers, and 

 even by M. Kendu (now Bishop of Anue^y), the author 

 of a most ingenious paper on glaciers, too little known. 2 

 Hugi perceived the errors arising from a confusion 

 between the rate of apparent advance of an increasing 

 ier into a warm valley, whilst it is continually being 

 shortened by melting, and the rate of motion of the ice 

 itself. 3 He points out the correct method of observation ; 

 and although his work contains no accurate measures, he 

 was perhaps the first who, by observing the position of a 

 ivniarkable block upon the glacier of the Aar, indicated 

 how such observations might be usefully made, instead of 

 trusting (as appears to have been the former practice) to 

 the vague reports of the peasantry. Hugi's observations 

 on the Glacier of the Aar give a motion of 2,200 feet in 

 nine years, or about 240 feet per annum. 4 Now, in 

 contradiction to this, it would appear from M. Agassiz's 

 observations, that from 1836 to 1839 it moved as far as 

 the preceding nine years that is, three times as fast. 5 

 There is reason, however, to think that M. Hugi's estimate 

 is the more correct/ 



' Bakcwrll 6 assigns 180 yards per annum as the motion 



of the Mer de Glace, and De la Beche 7 200 yards, on 



a in Shcrwill's authority. 8 But both of these were 



I Patchwork, i. 1 09. 



* Mem. de la Societe A cademique de Savaie t x. 95. 



'nreinr, p. 371. 4 Agassi z, KtmJcs, p. 150. 



I 1 hit!. ' [As conjectured in the text, Ilugi's estimate has been almost 

 exactly confirmed. Experience too has shown that the motion of 

 glaciers is almost uniform from year to year. (See 9th I.cttt r in the 

 Appendix.) The enormous error of his successors on the Glacier of 

 the Aar is therefore attributable to a want of the most ordinary ntti-n- 



1 ) accuracy, and shows how little such considerations were deemed 

 rtant by them.] ' 



44 i. nr,/i. ' GMofficmi Manual, p. 60. 



100 yardi, in rhiln*njih\c<d Magazine, Jan. 1 



