Description of the Rotascope. 271 



w, u, are nuts to keep in place the upper piece of the frame. Their 

 heads are perforated to receive cords for suspending the frame when 

 necessary. 



M, M, represent moving forces applied to the cord a, to give a 

 rapid motion to the wheel. To know precisely what forces are ap- 

 plied to this cord, in experiments requiring the measure of those 

 forces, we detach the weights W, W, and their cords c, c, bring down 

 the pullies p, p, nearly to the screws 5, s, and turning the rings into 

 such a position that the cord a will go over the pullies, substitute 

 weights of equal magnitudes at M, M, instead of the hands of the 

 experimenter. A double series of weights from two to thirty two 

 ounces accompanies the instrument. Each is furnished with a hook 

 at top, and a small conical pin at bottom ; the latter serving the 

 double purpose of keeping them in place when deposited on the base 

 of the stand, as seen in the figure, and of attaching them expedi- 

 tiously to the rings 1,2, by means of holes drilled to receive them. 

 A weight thus attached is seen at g, Fig. 2. 



The cord a, is attached to the axis by means of the small project- 

 ing conical knob k, k, one of which is near each end of the shaft. 

 The centre of the cord is doubled, and the pin applied to the doub- 

 led part, the wheel is then set in motion to wind up the cord, so that 

 one end vi^ill be drawn off from above, the other from below, and 

 both tend to turn the wheel in the same direction. 



c, c, are two cords connected with a small pulley on the axis of 

 ring 1, and passing over the pullies p, p. 



W, W, are weights attached to this cord. 



z indicates the direction in which those weights tend to turn the 

 ring 1. 



X denotes the direction in which the wheel will move when actu- 

 ated by the forces M, M, as here represented ; but by turning the 

 wheel in the opposite direction, when the cord is applied over the 

 knob, the wheel will be put in motion in the opposite direction. 



O is a bar of mahogany called the orbit-rod, with a socket/, by 

 means of which it may, when the frame F, is removed, be placed 

 on the pivot e, and made to revolve. In this case, the frame con- 

 taining the wheel, is to be set or suspended at one end, while at the 

 other is suspended tht3 weight C, which exactly counterpoises the 

 frame and its appurtenances. This weight is placed below the bar 

 in order to bring the centre of gravity as low as practicable, and pro- 

 duce a more stable equilibrium. 



