TORQUE, the twist or torsion which a shaft undergoes when transmitting power. The degree of twist is very slight, but it can be measured and the horse-power that is transmitted can thus be ascertained, the method being applied particularly to steam turbines. There are several types of torsion-meters for measuring horse-power, electrical, mechanical and flash-light. One of the last-named types is here described; its principle depends primarily on the straightness and very high velocity of a ray of light. Two discs are fastened to the shaft a measured distance apart. Each disc has a small slit in it, about in. by in., and a lamp is attached near one disc by a rigid support; the torque-finder is also rigidly secured. The light from the lamp is limited by a slit of similar size to those in the discs, and the torque-finder comprises a casting with a small telescopic eyepiece screwed to a brass plate which also has a slit of the same size as the others. The plate and eyepiece can be moved circumferentially by means of a micrometer apparatus, reading to .oi of a degree. If the lamp, discs and torque-finder are set
so that the four slits are in line, the observer looking through the eyepiece parallel to the axis of the shaft will see the light shining in the lamp. If the shaft starts to revolve, at each rotation as the two slits in the discs pass the sight line between lamp and finder the light will be seen momentarily. The persistence of this flash with the rapidly revolving shaft makes it appear as a continuous light. When however the shaft com mences to transmit power the torque throws the disc slits out of line and the light is obscured. The observer now adjusts the micrometer and the eyepiece until a sight is again taken through the disc slits. By noting the amount of the displacement thus made the degree of twist is measured, and therefrom the horse power transmitted. See DYNAMOMETER. (F. H.)