This line, like the third, was set out and numbered from the eastern side of the glacier, the theodolite occupying a position on the heights of the Echelets. A moment's inspection of the table reveals a fact different from that observed on the third line; there the most easterly stake moved with more than twice the velocity of the most westerly one; here, on the contrary, the most westerly stake moves with more than twice the velocity of the most easterly one.

To enable me to compare the motion of the eastern and western halves of the glacier with greater strictness, my able and laborious companion undertook the task of measuring with a surveyor's chain the line just referred to; noting the pickets which had been fixed along the line, and the other remarkable objects which it intersected. The difficulty of thus directing a chain over crevasses and ridges can hardly be appreciated except by those who have tried it. Nevertheless, the task was accomplished, and the width of the Mer de Glace, at this portion of its course, was found to be 863 yards, or almost exactly half a mile.

Referring to the last table, it will be seen that the two stakes numbered 12 and 13 moved with a common velocity of 231/4 inches per day, and that their motion is swifter than that of any of the others. The point of swiftest motion may be taken midway between them, and this point was found by measurement to lie 233 yards west of the dirt which marked the junction of the Glacier du Géant with its fellow tributaries: whereas, in the former cases, it lay a considerable distance east of this limit. Its distance from the eastern side of the glacier was 601 yards, and from the western side 262 yards, being 170 yards west of the centre of the glacier.

CONJECTURE TESTED.

But the measurements enabled me to take the stakes in pairs, and to compare the velocity of a number of them which stood at certain distances from the eastern side of the valley, with an equal number which stood at the same distances from the western side. By thus arranging the points two by two, I was able to compare the motion of the entire body of the ice at the one side of the central line with that of the ice at the other side. Stake 17 stood about as far from the western side of the glacier as stake 3 did from its eastern side; 16 occupied the same relation to 4; 15, to 5; 13, to 7; and 12, to 9.

Calling each pair of points which thus stand at equal distances from the opposite sides corresponding points, the following little table exhibits their comparative motions:—

Numbers and Velocities of Corresponding Points on the Fourth Line.

No. Vel.No. Vel.No. Vel.No. Vel.No. Vel.
West17 1516 171/415 221/413 231/412 231/4
East3 121/24 151/45 151/27 181/49 191/2

WESTERN HALF MOVES QUICKEST.

The table explains itself. We see that while stake 17, which stands west of the centre, moves 15 inches, stake 3, which stands an equal distance east of the centre, moves only 121/2 inches. Comparing every pair of the other points, we find the same to hold good; the western stake moves in each case faster than the corresponding eastern one. Hence, the entire western half of the Mer de Glace, at the place crossed by our fourth line, moves more quickly than the eastern half of the glacier.