Professor Joseph Henry's Invention 



longer wire offered to the conduction of electricit} 7 ". 

 Two methods of improvement therefore sug- 

 gested themselves. The first consisted, not in 

 increasing the length of the coil, but in using a 

 number of separate coils on the same piece of 

 iron. By this arrangement the resistance to the 

 conduction of the electricity was diminished and 

 a greater quantity made to circulate around the 

 iron from the same bat- 

 tery. The second 

 method of producing a 

 similar result consisted 

 in increasing the num- 

 ber of elements of the 

 battery, or, in other 

 words, the projectile 

 force of the electricity, 

 which enabled it to pass 

 through an increased 

 number of turns of wire, 

 and thus, by increasing the length of the wire, 

 to develop the maximum power of the iron. 



To test these principles oil a larger scale, the 

 experimental magnet was constructed, which is 

 shown in Fig. 6. In this a number of compound 

 helices were placed on the same bar, their ends 

 left projecting, and so numbered that they could 

 be all united into one long helix, or variously 

 combined in sets of lesser length. 



From a series of experiments with this and 

 other magnets it was proved that, in order to 

 produce the greatest amount of magnetism from 

 29 



