OF VULCANIZED INDIA-RUBBER.—HEBB. 275 
the kinetic method, the rigidity varied with the angle, and 
here, also, definite angles of twist were always used. 
In using the static method, the twisting force was applied at 
the end of the arm carried by the lower brass tube. In the 
earlier experiments it was applied by means of a thin silk 
string, horizontal and perpendicalar to the arm, which passed 
over the pulley of a set of frictionless wheels taken from an 
Attwood’s machine, and carried a small plummet of known 
weight. The plummet was so light that the cord was not 
appreciably deflected from the vertical. In order to make the 
friction as nearly as possible the same in all experiments with 
the same plummet, I observed the position of the end of the 
arm before the plummet was attached or the cord twisted, 
and then having attached the plummet, I determined the 
amount of twist to be applied in order that the arm might 
make small oscillations about this position. 
Even with this procedure, however, successive observations 
showed a lack of agreement which was traceable to friction. 
Hence, in the later experiments, I used Mallock’s* method of 
applying the force, which I found not only to give more con- 
sistent results, but to occupy less time. A small plummet of 
known weight which was suspended from the end of the arm 
by a fine silk string was drawn aside by a second silk string, 
which was kept horizontal, the two strings being in a plane 
perpendicular to the arm. The distance to which it was drawn 
aside was determined by the aid of a second plummet hanging 
freely from the end of the arm. The horizontal force at the 
end of the arm was then equal to the weight cf the first 
plummet multiplied by the ratio of the distance to which it was. 
drawn aside to the distance below the end of the arm of the 
point of junction of the two strings. These distances, 
together with the length of the arm, could be measured with 
consiacrable accuracy, and thus the torque to which the cord 
was subjected determined. 
* Proc. R. 8. L., 46, 233, 1889. 
