PEOFESSOE TTOT)ALL’S OBSEEVATIONS ON THE MEE HE GLACE. 
267 
Our next line (EE') stretched across the glacier from the promontory of Trelaporte to 
the base of the Aiguille du Moine. The instrument being placed upon a grassy slope 
above the promontory, the line was set out on the 28th of July. The Trelaporte end of 
this line was immediately under the station marked on the Map of Professor Foebes ; 
the displacements of the stakes were measured on the 31st of July, and were found to 
be as follows : — 
Fifth Line (EE'). — Mean Daily Motion. 
"West. East. 
No. of Stakes. 1 2 .3 4 5 6 7 8 9 10 11 12 13 14 15 
Motion Ill 131 12| 15 15i 16 ITJ 19i 19f 19 19i 171 16 14| 10 
The first of these stakes was about 80 feet distant from the face of the rock at Trela- 
porte ; the 15th was on the lateral moraine, which moved along with the ice at the 
opposite side of the valley. The retarding infiuence of both sides is very clearly shown, 
the motion of the central stakes being nearly twice that of the extreme ones. As a 
whole, the rate of motion is slower here than at the “ Fonts ” or at the Montanvert. 
This line was also chained by Mr. Hiest ; a copy of his notes, showing the distances 
along the line at which the stakes were set, faces this page. 
The chaining commenced at a point 116 links distant from the face of the rock at 
Trelaporte. Adding these 116 to the distance 3941, we have 4057 links, or 893 yards 
for the width of this portion of the Mer de Glace. The point of maximum motion 
occurs at stake No. 9, which is 2236 links distant from the rock at Trelaporte, or more 
than one-half the distance across ; that is to say, the point of maximum motion is here 
nearer to the Talefre side than to the Geant side of the glacier. Here, again, we have a 
result different from that obtained with our fourth line ; and if we look to the sketch-map 
we shall see the reason. Between the fourth and fifth lines the Mer de Glace has passed 
a point of contrary flexure ; and here at Trelaporte the convex side of the glacier is 
turned towards the base of the Aiguille du Moine. 
Taking the 116 links at the commencement into account, the following pairs of stakes 
may be regarded as corresponding points: — 3 and 14; 4 and 12; 7 and 10; the small 
numbers referring to stakes at the western, and the large numbers to stakes at the 
eastern side of the glacier. The relative motions of these points are as follows : — 
West 3— 12|; 4—15; 7—171. 
East 14— 14|; 12— 17^; 10—19. 
Comparing this Table with Table A, we observe a reverse result ; in the latter case the 
western stakes moved most swiftly; here the eastern ones do so; the deportment of the 
ice is the same as at the places intersected by our three first lines, and the curvature of 
the valley is also similar. 
Jrom the foregoing observations the following law of glacier motion is derived: — 
When a glacier moves through a sinuous valley, the locus of the point of maximum motion 
does not coincide with a line drawn along the centre of the glacier, hut always lies on the 
