530 THE LTFE OF JAMES D. FORBES. [APPEND. 



Cependant quand on agit sur un morceau de glace, qu'on le frappe, on lui trouve 

 unc rigidite qui est en opposition directe avec les appareuces dont nous venons 

 de parler. Peut-etre que les experiences faites sur de plus grandes masses 

 donneraient d'autres resultats." l Now it is by observations on the glacier itself 

 that we can best make experiments on great masses of ice, as here suggested.' 



(/) Travels, page 382. 'The idea of conparing a glacier to a river is 

 anything but new, and I would not be supposed to claim that comparison or 

 analogy as an original one. Something very like the conception of fluid 

 motion seems to have been in the minds of several writers, although I was not 

 aware of it at the time that I made my theory. In particular, M. Rendu, 

 whose mechanical views are in many respects more precise than those of his 

 predecessors or contemporaries, speaks of " glaciers d'ecoulement " as distinct 

 from " glaciers reservoirs ; " and in the quotation at the head of this chapter, 

 he evidently contemplates the possibility of the mutual pressures of the parts 

 overcoming the rigiditv. 2 He is the only writer of the Glacier school who has 

 insisted on the plasticity of the ice, shown by moulding itself to the endlessly 

 varying form and section of its bed ; and he is also opposed to his leading 

 contemporaries in his conjecture that the centre of the ice-stream would be 

 found to move fastest. But M. liendu has the candour not to treat his 

 ingenious speculations as leading to any certain result, not being founded on 

 experiments worthy of confidence. " The fact of the motion exists," he says ; 

 " tne progression of glaciers is demonstrated, but the manner of it is entirdi/ 

 unknown. Perhaps by long observations and well-made experiments on ice 

 and snow, we may be able to apprehend it, but these first elements are still 

 wanting." 8 .... [Here follows a quotation from Captain, Basil Hall.] 

 But such speculations could not pass into a theory until supported by the 

 definite facts of which M. Rendu deplores the want.' 



(g) Travels, p. 385. 'I have no doubt, however, that the convex 

 surface of the glacier (which resembles that of mercury in a barometer tube) 

 is due to this hydrostatic pressure acting upwards with most energy near the 

 centre. It is the "renflement" of Rendu, tne " surface bombeV' of Agassiz.' 



Such are the quotations from and references to M. Eendu in 

 the work which embodied the results of my own experiments 

 and speculations. In my later writings I did not suffer the 

 bishop's name to drop out of sight. 



1 ' Theorie des Glaciers de la Savoie, p. 84. Whilst I am anxious to show 

 how far the sagacious views of M. Rendu coincide with, as they also preceded 

 my own, it is fair to mention, that all my experiments were made, and indeed 

 by far the greater part of the present volume was written, before I succeeded 

 in obtaining access to M. Rendu's work, in the tenth volume of the Memoirs 

 of the Academy of Chambery, which I owe at length to the kindness of the 

 right reverend author.' * 



2 ' See also page 107 of his work for a comparison between a glacier and 

 a river.' 



3 ' " Le fait du mpuvement existe, la progression des glaciers est demontre'e ; 

 mais le mode est entierement inconnu. Peut-etre avec de longues observations, 

 des experiences bien faites sur la glace et la neige, viendra-t-on a bout de le 

 saisir : mais ces premiers elements nous manquent encore." ' 



* [I have explained already (page 9) that though I had cursorily seen M . llrixlu's 

 book in the possession of a friend, I never had access to it for consultation, 

 either while deducing my theory from observations on the glaciers themseh 

 afterwards, when elaborating it at home, until the time above referred to, which 

 was probably in February 1843. (I860.)] 



