332 ELECTRICITY. 



will, at the same time, turn round in the direction 

 opposite to that to which the points are turned. 



If the figures of horses, cut in paper, be fastened 

 upon these wires, and they be so contrived that 

 the points shall be in their tails, the experiment 

 will be more curious; the horses will seem to pur- 

 sue one another. It is possible to make several of 

 these wires, each having a considerable number of 

 points bent backwards, with horses, &c. fastened 

 to each of them 9 and turning one above another ; 

 and then some of them may be contrived to move 

 faster than the others. They may also be made to 

 move different ways. 



By means of the stream of electricity that issues 

 from a point, little models of machinery made of 

 stiff card may be set in motion. 



Plate 19. fig. 1., is an orrery for showing the 

 earth's motion round its axis in twenty-four hours, 

 the age of the moon from change to change, and 

 all her various phases during that time. A is the 

 horizontal board, or stand, of this machine ; and B 

 is the great wheel, with 18 floats, or wings, for the 

 electric stream to act upon, and turn the wheel, 

 according to the order of the letters a, b, c, d. On 

 the axis of this wheel is a trundle C of 8 staves for 

 turning the wheel F of 32 teeth, on whose axis is 

 a trundle G, of 8 staves, for turning the wheel H 

 of 59 teeth, which will go once round in the time 

 the great wheel A goes %9h A little hollow globe 

 D, representing the earth, with its meridians, &c. is 

 put upon the top of the axis of the great wheel A j 

 and on the same axis is the index E, which goes 

 round a small dial-plate e, of 24 hours, in the time 

 that the earth D turns round. An ivory ball, 1, is 

 placed on the top of the axis of the wheel H, half 

 black, half white, to represent the moon ; below 



