Professor Forbes on the Leading Phenomena of Glaciers, 247 



porting and confirming one another, lend strong countenance 

 to a theory which includes both. It would be very easy to 

 enlarge upon and multiply these illustrations and coincidences, 

 but I am satisfied that I have said enough to put the intelli- 

 gent reader in possession of the strong points of the theory, 

 whilst to many this chapter will appear already too long. A 

 few circumstances which have not been insisted on, appeared 

 in the letters to Professor Jameson, published in the Edin- 

 burgh New Philosophical Journal, October 1842, and January 

 1843. 



The idea of comparing a glacier to a river is any thing but 

 ■new, and I would not be supposed to claim that comparison 

 or analogy as an original one. Something very like the concep- 

 tion 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 pre- 

 decessors 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 pas- 

 sihility of the mutual pressures of the parts overcoming the 

 rigidity.* He is the only writer of the glacier school who has 

 insisted upon the plasticity of the ice, shewn by moulding it- 

 self to the endlessly varying form and section of its bed, and 

 he is also opposed to his leading contemporaries in his conjec- 

 ture that the centre of the ice-stream would be found to 

 move fastest. But M. Rendu 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 — " the progression of gla- 

 ciers is demonstrated ; but the manner of it is entirely unktiown. 

 Perhaps by long observations and well made experiments on 

 ice and snow, we may be able to apprehend it, hut these first 

 elements are still wanting.'''' ■\^ 



* See also page 107 of his work for a comparison betwteen a glacier and a 

 river. 



t " Le fait du mouvement existe, la progression des Glaciers est demontr^e ; 

 mais le mode est enti^rement inconnu. Peut-etre avec de longues observations, 



