A.] FORBES AND RENDU. 539 



des crevasses, qui sont en ge"ne"ral traiisversales sa direction. Si le mouve- 

 ment etait le meme dans toute la masse, ces crevasses, qui coupeut la surface 

 en ondees paralleles, formeraient une ligue droit qui serait touiours a peu pres 

 perpendiculaire aux deux rives ; mais il n'en est point ainsi ; la ligne generate 

 est une courbe dont la convexite s'avance vers le has de la valise, ce qui ne 

 peut etre attribue qu'a 1'exces de vitesse que les glaces ont sur ce point.' 

 REXDD, Thtorie, pp. 90, 97. 



From this extract we find very unexpectedly to the reader 

 of Professor Tyndall's account of Rendu's theory that the 

 Bishop relies for his conviction of the river-like motion of the 

 ice on an observation (if observation it was) altogether fallacious, 

 and from which a larger experience, and even a more impartial 

 study of the Mer de Glace alone, must have led him to draw a 

 consequence diametrically opposed to the plastic or river hypo- 

 thesis. It is now admitted by all parties, including Professor 

 Tyudall, 1 that, as a rule, the crevasses of a glacier stretch across 

 it in curves convex towards the origin. M. Agassiz and others, 

 misled in their deductions from this fact, which the-y recorded 

 correctly, espoused a false hypothesis. M. Rendu, having a just 

 hypothesis, observed the facts inaccurately, or must have relied 

 on some altogether local or apparent exception to a general law. 



The explanation of the whole matter is probably this : The 

 Bishop perceived the general river-like analogy of glaciers, which 

 had already struck Captain Hall and many other persons. He 

 ued forward to the conclusion, and viewed the facts with a 

 favourable bias. He seized on the inaccurate estimate of the 

 guides as to lateral retardation, without considering its improba- 

 bility, or ivlying on measures made either by himself or by 

 any educated person ; and ]\Q fancied that he saw in the direc- 

 tion of the crevasses in some portion of the glacier the desired 

 confirmation of the same view. This appears indeed to have 

 been his main reliance ; for in the comparison to a river, just 

 quoted, there is no mention of the guides' estimate ; and in a 

 lid passage further on (which I have referred to in my 

 irt, marked/), where he recalls in similar terms the points 

 of resemblance to a river, lie again recurs, for proof of the more 

 rapid central motion, to the form of tlw crevasses, and to that 



I hope that I have now satisfactorily shown that the two quo- 

 from Kcndu, t<> which Pinfcssor Tyudall attributes so 

 juificance, do not constitute any new claim in 1'avour of 



> Glacier* pt, p,. 32:? 



2 ' I^es ondees de glace marquees n:ir Irs crevasses transverealcs semblcnt sc 

 suivn ilit,' vcrs le milieu, cc fpii domic 



k ch;i !:i forim- d'un drmi-rrn-le 



ban de la N Nor is there a word of the guides' estimate of the lulrral 



iation. (Thiorie, p. 10?.) 



