1845.] ANALYSIS OF THE EXPERIMENT CONCLUDED. 117 



The beautiful convexity of the curves in the direction of 

 motion which the eye at once seized, and could more accurately 

 distinguish by the theodolite, as having its largest sagitta at the 

 twenty-fifth mark, namely, almost exactly midway between the 

 fourth mark or convex origin, and the forty-fifth or extreme 

 mark, contains in itself an evidence with which no person of 

 correct habits of thought can fail to be struck, as proving a 

 regular plastic action of gravity, or other propelling force, acting 

 from point to point on the mass of the glacier. I made, how- 

 ever, a check experiment almost unnecessary, but which I will 

 here detail. Lest it should be alleged that the whole area under 

 experiment was a moving one, capable of being swung round 

 by the pressure upon the centre of the glacier, so that the dis- 

 placement of the transverse line was due to rotation of the mass 

 operated on round some distant centre, I took care, near the 

 commencement of my experiment, to fix a mark in the ice in 

 the same line with Q parallel to the length of the glacier, or 

 perpendicular to the transverse visual line at the commencement 

 of the experiment. This point is marked q in Plate III. fig. 

 3. Now, had the block of ice on which the marks Q, q, (1), 

 (2), (3), etc., were fixed, been revolving round some fixed or 

 moveable centre, the right angle (3) Q q would have remained 

 a right angle, and so for (2) Q q and (1) Q q. But these angles 

 constantly became more obtuse, and that in different degrees 

 depending on the convexity of the curve Q, (1), (2), (3) ; and 

 so of (4) and (5). It is impossible, therefore, to avoid the con- 

 clusion, that the solid ice was itself distorted to the amount of 

 the excess of progression of the more central above the lateral 

 stations. 



The results are contained in the following Table, the five 

 stations being those formerly mentioned at 30, 60, 90, 120, and 

 180 feet from Q. The first three stations were fixed when the 

 visual line had an azimuth of 89 55' [reckoned] from q [as an 

 origin] ; the fourth was fixed on the 14th of August, when the 

 visual line had revolved through 3' (its daily progression towards 

 q in consequence of the translation of the station Q being 



