PEOFESSOE TYNDALL’S OBSEEVATIONS ON THE MEE DE GLACE. 
263 
On the 18th of July we set out a second line above the Montanvert Hotel, and we 
afterwards measured the displacements of the stakes along the line AA'. The result 
led to the estabhshment of a hitherto unobserved law of glacier motion, which the discus- 
sion of the observations will gradually render manifest. Reduced to twenty-four hours, 
the motion of the stakes along our first line was as follows - 
First Line (AA').— Mean Daily Motion. 
No. 
of stake. 
Motion in inches. 
No. of stake. 
Motion in inches. 
West 
1 . . 
. . . 121 
6 . . . 
• 
2 . . 
. . . 16f 
7 . . . 
. . 261 
3 . . 
. . . 221 
_ 8 . . . 
. 
4 . . 
. . . 251 
9 . . . 
. . 28f 
5 . . 
. . . 241 
East 10 . . . 
. . 351 
Stake No. 7 of this series was about midway between the bounding sides of the 
Mer de Glace ; No. 1 was near the lateral moraine at the Montanvert side, and the 
retarding influence of this side is very manifest. With slight breaches of regularity, 
the rate of motion increases gradually from the first stake towards the centre of the 
glacier. 
But it will be observed that stake No. 7 by no means moves the fastest. Stake 
No. 10 stood far beyond the centre, and upon the portion of the glacier derived from 
the Lechaud and Talefre. This portion is distinguishable at a glance by the quantity 
of dirt upon its surface, the portion derived from the Glacier du Geant remaining com- 
paratively clean throughout the entire length of the Mer de Glace. Professor Forbes 
accounts for the excessive crevassing of the eastern side of the glacier by assuming that 
the Glacier du Geant, having by far the greater mass, moves most swiftly, drags its 
more sluggish companions after it, and thus tears them asunder. The foregoing obser- 
vations show that this assumption is untenable. The difference here observed cannot 
be referred to the slip to which reference has already been made in the note at the foot 
of this page, for the slip did not amount to more than 4 inches at the utmost. Further, 
the displacements were measured a second time on the following day, when the maximum 
movement of the Glacier du Geant portion was found to be 27 ^ inches, and that of the 
Lechaud and Telefre side 32-|. 
Our second line, marked BB' upon the sketch-map, had its terminal station on the 
ancient moraine a little higher up the glacier than the Montanvert Hotel. Along this 
line thirty-one stakes were driven on the 18th of July, and their displacements 
measured the day following. The results reduced to twenty-four hours are as fol- 
lows : — 
of the ice ridges here, the whole mass slid suddenly some inches forward. Were special attention directed 
to the crevassed portions of a glacier, the same phenomenon might, I doubt not, be frequently observed. 
2 N 2 
