242 Contributions to Electricity and Magnetism. 



The wire conducting the secondary current is represented by b, that 

 conducting the tertiary by c, and the other wire, to receive the 

 induction from these, by d. The Pj .g 



direction of the influence, as be- 

 fore, is indicated by + — — 

 &c., and the third wire is again "^ + 



seen to be in \he plus region of ir"= ^■ 



the one current, and in the mi- o ^— ± A 



— + 

 mis of the other. If, however, _ + 



d is placed sufficiently near c, ~ "*" 



then neutralization will not take place, but the two currents will 



conspire to produce in it an induction in the same direction. A 



similar effect would also be produced were the wire c, in Fig. 15, 



placed sufficiently near the conductor b. 



133. Currents of the several orders were likewise produced 

 from the excitation of the magneto-electrical machine. The 

 same neutralizing effects were observed between these as in the 

 case of the currents from the galvanic battery, and hence we 

 may infer, that also the same alternations take place in the direc- 

 tion of the several currents. 



134. In conclusion, I may perhaps be allowed to state, that 

 the facts here presented have been deduced from a laborious series 

 of experiments, and are considered as forming some addition to 

 our knowledge of electricity, independently of any theoretical 

 considerations. They appear to be intimately connected with 

 various phenomena, which have been known for some years, but 

 which have not been referred to any general law of action. Of 

 this class are the discoveries of Savary, on the alternate magnet- 

 ism of steel needles, placed at different distances from the line of 

 a discharge of ordinary electricity,* and also the magnetic, screen- 

 ing influence of all metals, discovered by Dr. Snow Harris of 

 Plymouth.f A comparative study of the phenomena observed 

 by these distinguished sava7its, and those given in this paper, 

 would probably lead to some new and important developments. 

 Indeed every part of the subject of electro-dynamic induction 

 appears to open a field for discovery, which experimental industry 

 cannot fail to cultivate with immediate success. 



* Annales de Chimie et de Physique, 1827. 

 t Philosophical Transactions, 1831. 



