504 THE LIFE OF JAMES D. FORBES. [CHAP. 



behind, which form a new and endless glacier. The 

 mechanism may not inaptly be compared to that of the 

 modern paper machine, which, from the gradually con- 

 solidated material of pulp (representing the neve), at 

 length discharges, in a perpetual flow, the snowy web. 

 The theory of De Charpentier, on the other hand, repre- 

 sents the fabrication of the glacier going on within the 

 glacier itself, so that each part swells, and the dilatation 

 of each is added to that which acted upon itself, in order 

 to shove on the section of the ice immediately in advance. 

 In ihefwmer case, then, the distance between two deter- 

 minate points of the glacier remains the same ; in the 

 latter, it will continually increase. Again, on the former 

 hypothesis, the annual progress of any point of the glacier 

 is independent of its position ; on the latter , it increases 

 with the distance from the origin (the transverse section 

 of the ice being the same). The solution of this im- 

 portant problem would be obtained by the correct 

 measurement, at successive periods, of the spaces between 

 points marked on insulated boulders on the glacier ; or 

 between the heads of pegs of considerable length, stuck 

 into the matter of the ice, and by the determination of 

 their annual progress/ * 



' The more that I revolved the subject in my own 

 mind, the more clearly was I persuaded that the motion 

 of glaciers admitted of accurate determination, and must 

 lead to definite conclusions/ 



' We have seen that the motion of glaciers has been for 

 much more than half a century universally admitted as co- 

 physical fact. It is, therefore, most unaccountable that 

 the quantity of this motion has in hardly any case been 

 approximately determined. I rather think that the whole 

 of De Saussure's writings contain no one estimate of the 

 annual progress of a glacier, and if we refer to other 

 authors we obtain numbers which, from their variety and 

 inaccuracy, throw little light on the question. Thus, 

 Ebel gravely affirms 2 that the glaciers of Chamouni 



1 Edinburgh fteview, April 1842, p. 77. 



2 Guide du Voyageur, art. 'Glacier.' 



