ELECTRICAL APPARATUS. 



285 



upon a glass stand ; suffer a chain to fall from the prime 

 conductor to dip into the water ; turn the machine, and hold 

 a piece of bread to the swan, it will immediately turn to it, 

 and approach as if to eat the bread. Price, $0.50. 



Fig. 3-21. 



Fig. 322. 



Rolling Glass Halls. (Fig. 321, as above.) This instru- 

 ment for rolling glass balls is an admirable contrivance for 

 illustrating electrical attraction and repulsion. Three or 

 four glass balls made as light as possible, are supported on 

 an insulated glass plate, on the under part of which strips 

 of tin -foil are so pasted as to form a broad circle or border 

 near the margin, and four radii to that circle ; on the upper 

 part of the plate is a flat brass ring supported on small 

 glass pillars, so as to have its inner edge immediately over 

 the exterior edge of the tin foil. The brass ring being in com- 

 munication with the prime conductor, and the tin-foil with 

 the rubbers of the machine, the ring and foil will be oppo- 

 sitely electrified. The glass balls being attracted by the 

 ring, become positively electrified in the part which comes 

 in contact with it. Thus electrified, they will be attracted 

 by the foil, and communicating the charge, return to the 

 ring to undergo another change. Different parts undergo 

 in succession these changes, and the various evolutions of 

 the balls are very striking and curious. Price, $5.00. 



The Electrical Pail. (Fig. 322, as above.) This con- 

 sists of a small pail, two or three inches in diameter, with 

 a spout near the bottom, in which is a hole just large enough 



