he weight i connected to the poise k on the lower beam to act, drawing out the poise until the equilibrium is restored, when the weighted end of the lever falls, re-engaging the wheel; the poise indicating the exact weight equivalent to the force applied.
A fly l retards and equalizes the motion of the clock-work.
If greater force be then applied, the beam again rises, and the mechanism operates as before, until the crushing or breaking strain is reached.
In the machine designed by Colonel Flad, used for testing the stone employed in constructing the St. Louis bridge, the specimen is inserted into two collars, one at each end; one of these has a flat projection supporting a small vertical steel cylinder, which is pressed by a spring against a bar connected to the other collar, so that any compression or elongation of the specimen tends to turn the cylinder around.
On its top is a small mirror, which reflects the light of a lamp upon a graduated are concentric with the cylinder.