1845.] DETAILS OF THE EXPERIMENT ON THE MER DE GLACE. 109 



and those of (2) being 



1-17 1-12 1-16, 



the ratios are 



1-98 2-00 2-07. 



In like manner the ratios between (3) and (2) will be found to be 

 1-37 1-42 1-44. 



From these data the simultaneous relative motions of these 

 six stations may be projected in a curve, or rather polygon, as 

 shown in Plate IX. fig. 1, [of the Phil. Trans, for 1846.*] This 

 is interesting, as showing very plainly, not only the regulated 

 increase of swiftness of the glacier towards the centre, but that 

 the variation of the variation is clearly brought out, indicated by 

 a convexity in the direction of the motion, and confirming the 

 general principle long ago announced by me, that the retarda- 

 tion is relatively greatest towards the side, and less towards 

 the centre. I appeal to any one conversant with the laws of 

 mechanics in their practical application, whether the manifest 

 continuity of such a law does not plainly include a continuity 

 in the mutual action of the parts of the mass under experiment, 

 and even independent of the manifest absence of great disloca- 

 tions, would not establish the doctrine of a molecular yielding, 

 or plasticity in the ice, as opposed to the irregular justling of 

 great blocks, admitting that such could exist unperceived. 



The period through which this experiment extended (seven- 

 teen days) is conclusive against the idea that a small flexure 

 could take place until the accumulated strain on the solid pro- 

 duced a rupture, which relieved the strain, and so forth, per 

 saltum. The continuity of glacier motion in every case except 

 that of precipitous descents or ice-falls, first proved by my ex- 

 periments in 1842, is now universally admitted by those who 

 have had any personal experience in the measurement of glacier 

 motion, however opposed to my theoretical views, t The 



* [To estimate rightly the result of the projection, it requires to be made on a 

 rather inconveniently large scale. It has not therefore heen reproduced in this 

 volume j. 



f See proofs cited in my Ninth Letter on Glaciers, Edinburgh Philosophical 

 Journal, April 1845 [and page 68 of this volume]. 



