268 
PKOnSSSOE TYNDALL’S OBSEKVATIONS OS THE SIEE DE GLACE. 
convex side of the central line. It is therefore a curve more deeply sinuous than the 
<alley itself, and crosses the axis of the glacier at each point of contrary flame . 
rig. 2. 
The law may be illustrated by the foUowing experiraent :-A, 2 is a box filled 
fine mud which by raising a sluice in front flowed into the curr ed trough A hne 
"Lwn upon the mud above the bend, a second line, cd, below the bend and a 
third ef at the bend. The distortions of these three lines by the motion o e m 
downird wm rLeal the position of the point of maximum motion at the p^ 
cular places where they are drawn. The line ah was distorted to ah , the summit he 
curve being exactly in the centre of the trough, thus proving that the centre w^ t 
place of mLmum motion. The same was tme of the Ime cd, which was distoite o i. 
The line ef was distorted to df, the summit g of the curve being nearer to the side hf 
of the trough, this proving the point of maximum motion to he .owaids that . 
"ely know a case more calculated to impress the mind both with the yieldmg 
power of ice to pressure, and the magnitude of the forces brought “*<> P ^ 
of glaciers, than the crushing of the three tributaries of the Her 
thioat of the valley between Trelaporte and the base of the Aiguille du Home, ho 
wishing to trust the eyes in the estimation of cUstances here, each of the tliiee con uem 
branches was measured. The width of the Glacier du Geant, a sliort ihstaiice aboi e 
Tacul, was found to be 5155 links, or 1134 yards. The width of the Glacier ' 
iust before its junction with the Talefre, was found to be 3725 hnks, or 820 yaids. 1 at 
tf the Talbfre, before it is influenced by the pressure of the Lechaud, that ‘s. 
“ce^Lade, was found, approximately, to be 2900 links, or 638 yards Adtog a > 
together, we find the snm of the widths of the three branch glaciers to be 59/ .au . . 
At Trelaporte these three branches are forced through a gorge 893 yards m e, an o 
measurements show that it passes through with a velocity of nearl) 20 me les a ai . 
Limiting our view to one of the glaciers thus compressed, the facts appear still n 
astonishing. Previous to its junction with the Talefre, the Glacier de Lechaud has a 
width of thirty-seven chains and a half. In passing through the jaws o t le gram c 
le at Trelaporte, this hroad ice river is squeezed to a driblet f . 
ru,idth\ This fact illustrates the relation of the size and power of a glacier to the qua 
. If the defined line between X and Y on tbe sketch map represents a line drawn along the centre of the 
glacier, the dotted line will represent the locus of the point of maximum motion. 
