W. Mathews on Glacier-motion. 108 
past each other to the extent of a little less than the ;,';; of an 
ich at the sides, and the ;;';, of an inch at the center of the 
area under consideration. 
Mr. Reilly has not supplied me with any note of the motion 
of the edge of the glacier during the interval; but as the edge 
of the Great Aletsch was found to move at the rate of only an 
inch and a quarter in twenty-four hours, it probably did’ not 
exceed 2 feet. We shall therefore be justified in saying that 
while, in the right-hand moiety of the glacier, a differential 
motion of 10 inches is distributed over a width of 100 yards 
from the line of maximum velocity, a differential motion of at 
least 100 inches must be distributed over the remaining 70 yards 
up to the edge of the glacier. th 
Two of the thirty-feet spaces were staked out into subdivisions 
of 2 feet each. Hach of the intermediate stakes exhibited a 
differential motion, with occasional negative signs—the greatest 
relative displacement observed being 2°25 inches in the twenty 
ays, equivalent to the ;!; of an inch in twenty-four hours for 
points 1 inch apart. 
During the intervals of his labors on the Glacier of Bionassay, 
Mr Reilly ranged a line across the Mer de Glace, on the Cha- 
mouni side of the Montanvert. His measurements on this 
line during a period of nineteen days indicate a motion very 
similar in its character to that of the Glacier of Bionassay. 
The length of this line from the left-hand edge of the glacier 
to the point of maximum velocity was about 1000 feet. The 
central 500 feet had an absolute motion of 18 feet 7°75 inches 
motion to distribute over the lateral 500 feet of the line, or six 
umes as much as that of the central moiety. 
the observations above described is not new. It appears clearly 
from the measurements made by Professor Tyndall on the Mer 
read May 20, 1858, and published in vol. exlix of the Philoso- 
phical Transactions, But nowhere is it brought out with more 
