Gyroscope

an instrument constructed by M. Foucault to make the rotation of the earth visible. The principle on which it proceeds is this— that, unle gravity intervene, a rotating bedy will not alter the direction in which its permanent axis points, In the gyroscope there is a rotating metallic disk, the middle point of whose axis is also the center of gravity of the machine. By this device the action m U1. of gravity is eliminated. The instrument, moreover, is so constructed that - Vee v, rn <n GYROSCOPE, the axis of rotation can be made to point to some star in the sky. Then, 18 the heavy disk whirls round, it is found that the axis continues to point to the moving star, though, in consequence of this, apparently altering its direction relatively to bodies on the earth. If, again, the axis be point- 2d to the celestial pole, which is fixed, no alteration in its position relative to bodies on the earth takes place. The only feasible explanation of these appearances is that the earth is revolving on its axis.