of various pJumomena of Rotating Bodies. 273 



by means of the screw z it can be readily elevated, and pressed 

 against the semicircular piece xij attached to the collar os. In 

 this M^ay it is possible to fix mn at any inclination to the horizon. 

 When the screw z is loosened, the piece pu sinks by its own 

 weight, and the motion is once more free. 



In order to control the motion round the vertical axis, and 

 besides this to accelerate it or to retard it, a wire tu is screwed 

 into the piece ^j?^ at u. 



From m and n depend the wires ml and ni, on which different 

 weights, P, furnished with hooks, may be suspended. 



A wooden handle EF, to which two strings of equal lengths 

 .ire fastened at E and F, serves to set the discs AB and CD in 

 rotation. By winding these strings round the axes of the discs 

 either in the same or in opposite ways, it is possible to cause the 

 discs to rotate either in the same or in opposite directions, and 

 to impart to them velocities which are very nearly equal. 



When both are caused to rotate in the same direction, so that 

 they move as a single mass, and when the axis mn is perfectly 

 free to move, the axis retains its direction either without weights, 

 or when equal weights are placed at I and i. When on the one 

 side a greater M'eight is placed than on the other, the apparatus 

 moves round a vertical axis; and if the overweight be jjlaced at 

 m, the direction of rotation is opposed to what follows Avhen the 

 greater weight is placed at n. It is also evident that the direc- 

 tion of the motion is different according as the discs rotate in 

 the one or the other direction. When, in respect to an observer 

 situated in the production of mn, the motion is that of the hand 

 of a clock, the weight being attached to that side of the appa- 

 ratus which is nearest to the observer, then this side moves 

 from the right of the observer to his left. 



During this motion round a vertical axis, the inclination 

 towards the horizon is scarcely sensibly changed, even when 

 the one side sustains 2 lbs. or 1000 grms. more than the other. 

 Accelerating the rotation round the vertical axis by carrying the 

 rod tu round with the hand, the side on which the greater weight 

 rests is elevated ; whereas when the angular velocity of the ap- 

 paratus is retarded, the same side sinks. Checking this com- 

 pletely, by holding fast the rod to u, the ovenvcighted side falls 

 as low as possible. 



Permitting the apparatus weighted on one side, for example 

 at m, to rotate freely round the vertical axis, and clamping it 

 during its motion with the screw z in the exact inclination which 

 It has assumed towards the horizon, the rotation round the ver- 

 tical axis ceases, but begins again immediately, provided the 

 discs AB and CD persist in their rotation, when the screw z is 

 loosened. Care must, liowever, be taken in loosening the screw 



