PEOFESSOE TYNDALL’S OBSEEVATIONS ON THE MET? DE OLACE. 269 
tity of snow drainage which supplies it. The Talefre has its basin, and the Geant has 
its vast plateau, from which the respective glaciers derive nutrition ; but the Lechaud is 
fed by two or three couloirs merely, which descend principally from the Mont Mallet 
and Les Jorasses. The Geant, in the struggle for place at Trelaporte, takes up more 
than half the valley, and the others come in the order of the drainage which supplies 
them. 
The velocity of the Mer de Glace at Trelaporte being about 20 inches, it seemed pro- 
bable that the velocity of the Glacier du Geant above the Tacul, and also of the Lechaud 
above its junction with the Talefre, would be considerably less, in consequence of the 
greater width at these places. This proved to be the case. On the 29th of July a line 
was set out across the Glacier du Geant, a little above the Tacul. There were ten stakes 
in this line, and their motions reduced to twenty-four hours were as follows : — 
Sixth Line (HH'), — -Mean Daily Motion. 
No. of Stakes. 12 34 5 6 7 89 10 
Motion 11 10 12 13 12 12f IQi 10 9 5 
The velocity here is considerably under that of the Mer de Glace at Trelaporte. 
On the 1st of August we set out a line across the Glacier de Lechaud immediately 
above where it is joined by the Talefre. The line commenced at the side of the glacier 
beneath the block of stone called the Pierre de Beranger, and ran perpendicular to the 
axis of the glacier to the other side. The displacements were measured on the 3rd of 
August : reduced to twenty-four hours, they are as follows : — 
Seventh Line (KK'). — Mean Daily Motion. 
No. of Stakes. 1 2 345 6 7 89 10 
Motion 4i 81 91 9 81 7i 6i 8i 7 5i 
The stakes 8 and 9 were at opposite sides of a “ moulin,” which was found to share 
the general motion of the glacier. A new crevasse crossed our line above 8 and below 
9, and the greater advance of stake No. 8 was probably owing to the yielding which 
this crevasse permitted. The rates of motion, it will be observed, are still less than 
those upon the Glacier du Geant. 
"Were the Glacier de Lechaud subjected to no waste during its descent, and did no 
accumulation take place at any point, equal quantities of ice would pass through all 
its cross sections in the same time. The compression which takes place at Trelaporte 
is not a change of volume but of form. The mass is squeezed laterally, and no doubt 
expands vertically. Comparing the velocities and widths at Trelaporte and opposite the 
Pierre de Beranger, we should be led to the result that the depth of the Glacier de Le- 
chaud at the former place would, if no waste had taken place, be at least four and a half 
times its depth at the latter. The loss of ice by superficial and subglacial melting must 
materially modify this result ; but some interesting observations might be made in con- 
MDCCCLIX. 2 0 
