Polytechnic Association Proceedings. 997 



longer coil for the secondary current than that used to transmit the 

 battery current, and also in producing shocks from a purely second- 

 ary coil exterior to the primary coil.* 



The next induction coil we find to be that of Prof. Callan, of 

 Maj'nooth College, Ireland, allusion to which has been before made. 

 Prof. Callan's description of this coil is found in the London and 

 Edinburgh PJiilosopJdcal Magazine for December, 1836. This 

 communication is dated August 23, 1836. Prof. Callan's coil is w 

 described as consisting of two coils of copper wire, wound upon 

 a bar of iron two feet long, and one inch in diameter. "These 

 wires were in two lengths of 200 feet each, of the same size, and 

 the end of the first coil and the beginning of the second were im- 

 mersed into the same cup of mercury — the voltaic current was 

 passed through the first coil only, and the shock taken by making 

 a communication with the beginning of the first coil, and with the 

 end of the second." It was not stated whether one coil was exterior 

 to the other, or whether they were side by side on different portions 

 of the bar. The mode of obtainhig the intensity current from the 

 secondary current was precisely a repetition of that of Prof. Page's. 

 No mention is made by Prof. Callan of a shock or a current from 

 the purely secondary circuit. 



In the April No. of Sturgeon^s Annals for 1837, Prof. Callan 

 communicated a brief article describing a complicated mechanical 

 contrivance for breaking the primary circuit with rapidity, so as to 

 obtain shocks from the electro-magnet. In the course of this article, 

 he speaks of the thick wire for the primary, and thin wire for the 

 secondary circuit, but does not give the length of either. The 

 communication was without date. Thin or fine wire is purely a 

 relative expression, but here is meant a wire for the secondary 

 smaller than that used for the primary circuit. We are unable to 

 trace accurately the history of the introduction of fine wires for 

 intensity circuits. The wire in common use for conductors and 

 coils, from the commencement of experiments in electro-magnetism, 

 was bell wire, or No. 16, which is about one-sixteenth of an inch - 

 thick; and unless authors specify the diameters of wires, we take it 

 for granted that copper wire means bell-wire size. Mr. Clarke, the 



* Prof. Page, at the time of this announcement, was a medical student, and had no facili- 

 ties at that time for obtaining a knowledge of the progression of electrical science in 

 Europe. Information, however, of Prof. Page's experiments was carried to Europe, 

 by Francis Peabody, of Salem, Mass., and communicated to Mr. Sturgeon in advance of 

 their publication here. 



