274 ON THE RIGIDITY 
the cut ends of these brass tubes and firmly fastened there by 
wire twisted around the tubes outside. Cords of considerable 
length were used, in order that the effect of the gripping at the 
ends might be inappreciable. 
The cords were suspended from an iron bracket, moveable 
on vertical guide-posts which were attached to the wall of the 
laboratory, and capable of being firmly clamped to these posts 
at any desired elevation. 
The upper brass tube passed through a wooden socket 
firmly fixed in the bracket. It was held in this socket by 
friction, and while it could be rotated by hand, there was no 
danger of its shifting its position otherwise. The brass tube. 
projected above the socket, and carried a wooden disk, on which 
was a divided circle. A pointer fixed over the disk indicated 
the number of degrees through which the cord was twisted. 
Thus any desired torsion could be given to the cord at the. 
upper end. 
The brass tube at the lower end of the cord carried, in a 
plane perpendicular to it, a light wooden arm for the application 
of the twisting force in the static experiments, and which 
served as a platform for the stretching weights. 
These weights were square leaden plates of about four 
inches’ edge. They had holes of the size of the brass tube cut 
in the centres, and slits leading to them from the edge, so that. 
they could be easily put on and taken off. 
In applying the kinetic method, the cord was kept fixed at 
the top, while the lower end, with the plates attached, was 
twisted through some angle and then let go. The time of 
oscillation was then determined by means of a stop-watch. 
This datum, together with other data easily obtained, viz., 
length and diameter of cord, and moment of inertia of plates, 
gave the means of finding the rigidity. In determining the 
time of oscillation, it was soon noticed that it varied with the 
angle through which the eord was twisted. Hence the cord 
was always twisted through known angles. In the static, as in 
