282 BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



Fig. 316. 



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Electrical Orrery. (Fig. 316.) This apparatus is seen 

 above. It represents the sun, earth, and moon. The 

 earth and moon are balanced at their centre of gravity, 

 upon a pointed wire, bearing at its other end the sun : this 

 wire has a point projecting sideways near its furthest extre- 

 mity. The moon also bears a side point, thus (every part 

 being nicely balanced), the earth and moon revolve round 

 each other, and both together round the sun making one 

 of the best possible illustrations of the real motion of these 

 heavenly bodies. Price, $2.50. 



The Electrical In- 

 clined Plane. (Fig. 

 317) This is a beauti- 

 ful experiment, and sa- 

 tisfactorily shows that 

 the electrical matter is- 

 suing from a number 

 of points possesses force 

 sufficient to counteract 

 the power of gravity in light bodies. It consists of a board 

 of mahogany, fourteen inches long and four inches broad, 

 having four glass pillars, three-tenths of an inch in thick- 

 ness ; the length of the two longer is seven inches, and 

 that of the two shorter is five inches. 



From the longer to the shorter pillars are stretched two 

 fine brass wires, parallel to each other, and tightened by 

 screws which pass through the brass balls which surmount 



