OF ARTS AND SCIENCES. 



233 



a plate of smoked glass which slides to and fro with a flat board m n. 

 The latter moves in guides, d is a brass pointer, which presses against 

 the smoked glass and moves to and fro at right angles to the direction 

 of the board m n. Two eccentrics connected with the wheels L and E 

 communicate the to and fro motions to the pointer d and the glass A. 



Fig. 1. 



This glass is placed in front of the projecting lantern, and the curves 

 of Lissajous are thus drawn on a screen before an audience. By 

 changing the position of the eccentrics, the size of the curves can be 

 modified at pleasure. A pulley, p, which slides in guides and can be 

 clamped at any point, gives the connecting belt the requisite tension. 



I gg^P A 4- -— 13 



Fig. 2. 



The rate of the movement at E can be changed by the device shown 

 in Fig 2. E is the face of the wheel to which the eccentric is at- 

 tached. This face is affixed to the end of a slotted shaft which forms 

 the centre of an axle, A B. At one end of this axle is the frustum of 

 a cone, C D, which is provided with grooves for the leather string 

 which serves for a belt to connect the arrangement at E with that at 

 L, Fig. 1. By this arrangement, the same string can be used when 

 the ratio of the wheels is changed ; which is done by slipping both the 



