To complete our knowledge of the motion of the Mer de Glace, we afterwards determined the velocity of its two accessible tributaries--the Glacier du Geant, and the Glacier de Lechaud. On the 29th of July, a line of stakes was set out across the former, a little above the Tacul, and their motion was subsequently found to be as follows: Sixth Line.--Daily Motion. No. of stake. Inches. 1 moved 11 2 " 10 3 " 12 4 " 13 5 " 12 6 moved 12-3/4 7 " 10-1/2 8 " 10 9 " 9 10 " 5 The width of the glacier at this place we found to be 1134 yards, and its maximum velocity, as shown by the foregoing table, 13 inches a day. On the 1st of August a line was set out across the Glacier de Lechaud, above its junction with the Talefre: it commenced beneath the block of stone known as the Pierre de Beranger. The displacements of the stakes, measured on the 3rd of August, gave the following results:-- Seventh Line.--Daily Motion. No. of stake. Inches. 1 moved 4-1/2 2 " 8-1/4 3 " 9-1/2 4 " 9 5 " 8-1/2 6 moved 7-1/2 7 " 6-1/4 8 " 8-1/2 9 " 7 10 " 5-1/2 The width of the Glacier de Lechaud at this place was found to be 825 yards; its maximum motion, as shown by the table, being 9-1/2 inches a day. This is the slowest rate which we observed upon either the Mer de Glace or its tributaries. The width of the Talefre-branch, as it descends the cascade, or, in other words, before it is influenced by the pressure of the Lechaud, was found approximately to be 638 yards. [Sidenote: SQUEEZING AT TRELAPORTE.] The widths of the tributaries were determined for the purpose of ascertaining the amount of lateral compression endured by the ice in its passage through the neck of the valley at Trelaporte. Adding all together we have-- Geant 1134 yards. Lechaud 825 " Talefre 638 " Total 2597 yards. These three branches, as shown by the actual measurement of our 5th line, are forced at Trelaporte through a channel 893 yards wide; the width of the trunk stream is a little better than one-third of that of its tributaries, and it passes through this gorge at a velocity of nearly 20 inches a day. [Sidenote: THE LECHAUD A DRIBLET.]