[§ 27.] Motion of Tributary Glaciers.
194. So much for the trunk glacier; let us now investigate the branches, permitting, as we have hitherto done, reflection on known facts to precede our attempts to discover unknown ones.
195. As we stood upon our "cleft station," whence we had so capital a view of the Mer de Glace, we were struck by the fact that some of the tributaries of the glacier were wider than the glacier itself. Supposing water to be substituted for the ice, how do you suppose it would behave? You would doubtless conclude that the motion down the broad and slightly-inclined valleys of the Géant and the Léchaud would be comparatively slow, but that the water would force itself with increased rapidity through the "narrows" of Trélaporte. Let us test this notion as applied to the ice.
196. Planting our theodolite in the shadow of Mont Tacul, and choosing a suitable point at the opposite side of the Glacier du Géant, we fix on July 29 a series of ten stakes across the glacier. The motion of this line in twenty-four hours was as follows:—
MOTION OF GLACIER DU GÉANT.
Sixth Line: H H' upon Sketch.
| Stake | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| Inches | 11 | 10 | 12 | 13 | 12 | 13 | 11 | 10 | 9 | 5 |
197. Our conjecture is fully verified. The maximum motion here is seven inches a day less than that of the Mer de Glace at Trélaporte ([192]).
198. And now for the Léchaud branch. On August 1 we fix ten stakes across this glacier above the point where it is joined by the Talèfre. Measured on August 3, and reduced to twenty-four hours, the motion was found to be—