264 
PEOFESSOE TYNDALL’S OBSEEVATIONS ON THE ZVLEE DE GLACE. 
Second Line (BB').~Mean Dady Motion. 
No. of stake. 
Motion in inckes. 
No. of stake. 
West 1 . . 
. . • • 2 
17 . 
2 . . 
. . . lOf 
18 . 
3 . . 
... 121 
19 . 
4 . . 
. . . 14i 
20 . 
5 . . 
. . . 14i 
21 . 
6 . . 
... 16 
22 . 
7 . . 
. . . 16f 
23 . 
8 . . 
... 171 
24 . 
0 . . 
... 19 
25 . 
10 . . 
. . . 19i 
26 . 
11 . . 
... 191 
27 . 
12 . . 
... 21 
28 . 
13 . . 
... 21 
29 . 
14 . . 
... 21 
30 . 
15 . . 
... 221 
East 31 . 
16 . . 
... 221 
Motion in inclies. 
. . 22i 
. . 21 
. . 22i 
. . 20i 
. . X 
. . X 
. . 2 ^ 
. . X 
. . 21f 
. . X 
. . X 
. . 22i 
. . 22f 
. . 25J 
. . 25f 
The stakes marked thus X were fixed by the eye, their positions being such that they 
could not be seen by the theodolite. Some of them were placed in deep glacial hollou s. 
where, without an instrument, it was difficult to keep them in the same vertical plane 
The slight uncertainty thus arising induced me finally to reject them. le gia m. 
augmentation of velocity from the side towards the centre is very manifest; but it ui 
be observed that stake 31, which stood upon the Talefre side of the glacier, move 
quickest of all. The difference in favour of the latter side is, however, much less than 
it was lower down. 
The reason why in the two cases just considered the terminal stake towards the eas ein 
side of the glacier shows no retardation, is, that the state of the ice, and the position o 
the theodolite, were not such as to enable us to continue the line of stakes completely 
across the glacier to the eastern side, and hence the observations could not show t it le- 
tarding influence of that side. In setting out the third line CC', therefore, Mr. Hikst 
took up a position on the Chapeau side of the valley, from which the vision across the 
o-lacier was quite uninterrupted by ridges or other obstacles, while the crevasses weie 
not impracticable. One of the fixed termini of this line was the corner of a wmidow 
of the Montanvert Hotel. There were twelve stakes planted along the line, and tlie 
motion of these during twenty-four hours, from the 20th to the 21st of July, was a. 
follows : — 
