ELECTRO-MAGNETISM. 121 



be floated on acidulated water, by means of a cork, 

 and submitted to the same experiment. In this con- 

 struction, the wires proceeding from the end of the 

 coil, pass through the cork, before connecting with the 

 metallic plates. The first described method of suspen- 

 sion is regarded as the best. 



288. THE COIL A MAGNETIC NEEDLE. 



How may the 



coil be conver- On floating a coil with extreme deli- 



<=acy upon water, and protecting it from 

 all currents of air and water, it assumes 

 north and south direction, and becomes, in fact, a mag- 

 netic needle. This can only be accomplished by 

 means of a light glass cup, blown for the especial pur- 

 pose, and prolonged into a cone below, to give it stead- 

 iness in the water. This cup is filled with dilute acid, 

 in which the plates are immersed, and is then floated 

 in a larger vessel. 



289. MUTUAL ACTION OF COILS. Two 



Describe the . 



mutual action helices, or coils, such as are described in 



the last paragraph, floating near each other, 

 attract or repel, precisely as if they were 

 magnets, according as like or unlike poles are brought 

 together. They finally attach themselves to each 

 other in the position represented in 

 the figure, lying parallel and with 

 opposite poles in contact. In this 

 position, it will be observed, that at thepoint of con- 

 tact, the currents are moving in the same direction. 

 The attraction of the unlike poles, may be regarded, 

 then, as a consequence of the attraction of like cur- 

 rents. For it is found to be universally true, that 



6 



