- + 



— + 



336 CONTKTBUTIONS TO ELECTRICITY AND MAGNETISM. 



hence the two actions neutralize each other, and no apparent result is 

 produced. 



132. Fig. 16 indicates the method in which the neutralizing effect 



p. j^ is produced in the case of the secondary 



and tertiary currents. The wire conduc- 



+ ; 1 ting the secondary current is represented 



^~ c by b, that conducting the tertiary by c, 



o + d and the other wire, to receive the induc- 



— + ^ ' 



tion from these, by d. The direction of 

 the influence, as before, is indicated by 

 -|- — — , &c., and the third wire is again seen to be in the plus re- 

 gion of the one current, and in the minus of the other. If, how- 

 ever, d is placed sufficiently near e, then neutralization will not take 

 place, but the two currents will conspire to produce in it an induc- 

 tion 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 alter- 

 nations take place in the direction 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 elec- 

 tricity, 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 gene- 

 ral law of action. Of this class are the discoveries of Savary, on the 

 alternate magnetism of steel needles, placed at different distances from 

 the line of a discharge of ordinary electricity,* and also the magnetic, 

 screening influence of all metals, discovered by Dr Snow Harris of Ply- 

 mouth. f A comparative study of the phenomena observed by these 

 distinguished savants, and those given in this paper, would probably 



* Annales de Chimie etde Physique, 1827. 

 t Philosophical Trausaclions, 1831. 



