110 VISCOUS THEORY OF GLACIEK MOTION. [1845. 



changes for seventeen days were connected (as has been shown) 

 by a law of continuity established by numerous intervening ob- 

 servations ; and the flexure or distortion of the ice amounted in 

 this time to no less than four feet at the opposite ends of a line 

 180 feet in length. It is quite certain, from my own previous 

 observations and those since made by M. Agassiz's directions on 

 the glacier of the Aar, that the movement thus shown to have 

 continued seventeen days without a saltus would have continued 

 the whole season in the same manner. In fact, the deformation 

 or flexure thus observed being sufficient to account for the whole 

 excess of the central arbove the lateral motion, is in itself an 

 explanation, and a proof that the explanation is adequate, and 

 leaves nothing residual to be accounted for by saltus.* 



I have more to add on this subject, but shall first give an 

 account of an extension of this experiment on the actual flexure 

 of the ice, upon so elaborate a scale as I scarcely ventured to 

 hope would prove successful, especially as the time I could 

 devote to watch its progress was small, and the circumstances 

 of weather excessively unfavourable. 



Having succeeded so well with the thirty feet station in the 

 transverse line, I thought of multiplying the points of observation 

 still further, so as to obtain a polygon of flexure more nearly 

 approaching to a curve. This I did by making the first ninety 

 feet of the transverse line, *. e., the space between Q and (3), 

 Plate III. fig. 3, the subject of more immediate experiment, 

 fixing in it forty-five stations only two feet apart. After seve- 

 ral partial failures, which gave me, notwithstanding, encouraging 

 results, I selected this plan : a space a foot wide and ninety 

 feet long, was cleared with hatchets and ice tools, so as to 

 arrive at a nearly even surface of the hard delicately-veined ice ; 



* Mr. Williamson, Fellow of Clare Hall, Cambridge, to whom I proposed this 

 experimental test of the theory of movement by echelons, made a series of independ- 

 ent observations on the Mer de Glace, which coincided in result with what has been 

 stated above. After a patient examination of these facts, and of others which he 

 observed on different glaciers, I am glad to say that Mr. Williamson was led to 

 abandon the theory of sliding columns or fragments, and to accept that of plasticity 

 as connected with the mechanism of the veined structure which I have endeavoured 

 to illustrate above. 



