ELECTRO-MAGNETIC INSTRUMENTS. 

 Fig. 444. 



25 



instrument. On passing the battery current through the 

 coil, the ends become similar poles, and the middle & an op- 

 posite pole. And by changing the direction of the current 

 the poles will be reversed. Price, $3.00. 



Magnets revolving Fig- 445. 



round a Wire. 

 (Fig. 445.) This 

 consists of two flat 

 bar magnets, dou- 

 bly bent in the mid- 

 dle, and having at 

 the under part of 

 the bend agate cups 

 fixed, by which they 

 are supported up- 

 on upright pointed 

 wires, affixed in the 

 basis of the appa- 

 ratus, and upon 

 which they turn 

 round as upon an 

 axis. Above the 

 agate cups, on the 

 upper part of the 

 bend, small cisterns 

 to hold mercury are 

 also formed. Two 

 circular troughs to 

 contain mercury, are supported upon a stage, affixed to the 

 basis, having holes in their centres to allow the magnets to 

 pass through them. A bent pointed wire is affixed into the 

 VOL. II. 3 



