A.] FORBES AND RENDU. 527 



definite probability on the evening of the 24th July, 1842, when 

 from the heights of the Charmoz I saw the dirt-bands stretching 

 across the breadth of the Mer de Glace at my feet, like floating 

 scum on a partially stagnant stream, such as I have described at 

 page 162 of my Travels in the Alps ; and from that hour the 

 viscous or plastic theory was to me a conviction and a reality. 1 

 I will not at this date hazard an assertion as to the exact period 

 at which I coupled with this thought the hitherto slighted 

 speculation of the Canon of Chambery. I will therefore, in my 



ment, rely only on documentary evidence. On the 22nd 

 August I made the following remark in a letter to Professor 

 Jameson, written from Zermatt, in which I expounded the lead- 



: matures of my own theory : ' It is not difficult to foresee, 

 that if my view should prove correct, a theory of glaciers may 

 be formed which, without coinciding either with that of Saussure 



iiarpentier, shall yet have something in common with both. 



her that of M. Rendu may not avail something, I am 

 unable to say, not yet having been able to procure his work.' 2 



Thus far, at least, there is no tendency manifest on my part to 

 suppress the fact that M. Rendu had a theory, and that it might 

 probably bear upon mine. 



Knowing just so much as I then did of M. Rendu's book, had 

 I wished to maintain a colourable ignorance of its contents, 

 I might have proceeded to develop tranquilly my own theory. 

 But I find (again appealing to documentary evidence for what 

 would otherwise have unquestionably escaped my memory), that 

 both in Switzerland and at Turin (whither I went in the summer 

 <>t 1842) I sought for Rendu's work in vain, and requested 

 Abbe Baniffi at the latter place to do me the favour of writing 

 to his brother ecclesiastic to obtain a copy for me. 



Notwithstanding all this, I returned to Edinburgh in the 

 autumn of 1842, and commenced writing my 'Travels,' with the 



imfortable feeling that I had now procured and read every 

 book about glaciers which I knew or had heard of, except the 

 one whose contents it might prove to be most important for me 

 to know. 



1 See my Third Letter on Glaciers, dated 22nd August 1842, where tbe 

 following passages occur : 'One afternoon I happened to ascend higher than 

 above the level of the Mer de (ilaee, and was struck by the anpcaranee 

 if discoloured bauds traversing its surface nearly in the form indicated in 

 Iff. 4. dirt-bauds perfectly resemble those of froth and scum 



rnich every one has seen upon the surface of slowly moving foul water ; and 

 the idea of fluid i,, t in the middle and 



tructcd l>v friction towards the sides and bottom.' OoconOftoJ J'nfnrt on 

 -.< (1859), pp. 21, 23. 



Appendix, 

 (1S59), p. 24. 



