42 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



lices, or electro-magnets, used to complete the circuit, were made or broken. These 

 cups I will call G and E throughout the rest of this paper (1079.). 



1053. Certain helices were constructed, some of which it will be necessary to de- 

 scribe. A pasteboard tube had four copper wires, one twenty-fourth of an inch in 

 thickness, wound round it, each forming a helix in the same direction from end to 

 end ; the convolutions of each wire were separated by string, and the superposed 

 helices prevented from touching by intervening calico. The lengths of the wires 

 forming the helices were 48, 49*5, 48, and 45 feet. The first and third wires were 

 united together so as to form one consistent helix of 96 feet in length ; and the se- 

 cond and fourth wires were similarly united to form a second helix, closely inter- 

 woven with the first, and 94*5 feet in length. These helices may be distinguished by 

 the numbers i and ii. They were carefully examined by a powerful current of electri- 

 city and a galvanometer, and found to have no communication with each other. 



1054. Another helix was constructed upon a similar pasteboard tube, two lengths 

 of the same copper wire being used, each forty-six feet long. These were united into 

 one consistent helix of ninety-two feet, which therefore was nearly equal in value to 

 either of the former helices, but was not in close inductive association with them. 

 It may be distinguished by the number iii. 



1055. A fourth helix was constructed of very thick copper wire, being one fifth of 

 an inch in diameter ; the length of wire used was seventy-nine feet, independently of 

 the straight terminal portions. 



1056. The principal electro-magnet employed consisted of a cylindrical bar of soft 

 iron twenty-five inches long, and one inch and three quarters in diameter, bent into 

 a ring, so that the ends nearly touched, and surrounded by three coils of thick copper 

 wire, the similar ends of which were fastened together ; then each of these termina- 

 tions was soldered to a copper rod, serving as a conducting continuation of the wire. 

 Hence any electric current sent through the rods was divided in the helices surround- 

 ing the ring, into three parts, all of which, however, moved in the same direction. The 

 three wires may therefore be considered as representing one wire, of thrice the thick- 

 ness of the wire really used. 



1057. Other electro- magnets could be made at pleasure by introducing a soft iron 

 rod into any of the helices described (1053. &c.). 



1058. The galvanometer which I had occasion to use was rough in its construction, 

 having but one magnetic needle, and not at all delicate in its indications. 



1059. The effects to be considered depend on the conductor employed to complete 

 the communication between the zinc and copper plates of the electromotor ; and I 

 shall have to consider this conductor under four different forms : as the helix of an 

 electro-magnet (1056.) ; as an ordinary helix (1053. &c.) ; as a long extended wire, 

 having its course such that the parts can exert no mutual infliuence ; and as a short 

 wire. In all cases the conductor was of copper. 



1060. The effects are best shown by the electro-magnet (1056.). When it was 



