Fifth Line: E E' upon the Sketch.

WestEast
Stake123456789101112131415
Inches111413151516171920192018161510

179. Here, again, the mere estimate of distances by the eye would show us that the three stakes which moved fastest, viz. the 9th, 10th, and 11th, were all to the east of the middle line of the glacier. The demonstration that the point of swiftest motion wanders to and fro across the axis, as the flexure of the valley changes, is, therefore,—shall I say complete?

180. Not yet. For if surer means are open to us we must not rest content with estimates by the eye. We have with us a surveying chain: let us shake it out and measure these lines, noting the distance of every stake from the side of the glacier. This is no easy work among the crevasses, but I confide it confidently to Mr. Hirst and you. We can afterwards compare a number of stakes on the eastern side with the same number of stakes taken at the same distances from the western side. For example, a pair of stakes, one ten yards from the eastern side and the other ten yards from the western side; another pair, one fifty yards from the eastern side and the other fifty yards from the western side, and so on, can be compared together. For the sake of easy reference, let us call the points thus compared in pairs, equivalent points.

181. There were five pairs of such points upon our fourth line, D D', and here are their velocities:

Easternpoints;motionininches1315161820
Western""""1517222323

In every case here the stake at the western side moved more rapidly than the equivalent stake at the eastern side.

182. Applying the same analysis to our fifth line, E E', we have the following series of velocities of three pairs of equivalent points:—

Easternpoints;motionininches151819
Western""""131517

183. Here the three points on the eastern side move more rapidly than the equivalent points on the western side.