DOVE ON THE ELECTRICITY OF INDUCTION. 157 



of the other metal. It would however be premature to arrange 

 the metals in a series at present. 



VII. Influence of the presence of iron on induced currents 

 of higher orders. 



A current induced by the connecting wire of a galvanic or 

 an electric battery can, as Henry* has lately shown, be again 

 used as a primary current, and thus induce a second current, 

 this again a third, and so on. Henry employed for the exa- 

 mination of these currents flat spiral coils ; all his experiments 

 are therefore only electro-dynamical. The question, whether the 

 principle of increasing the power by means of bundles of wires 

 was applicable to these currents, appeared to me worthy of inves- 

 tigation for two reasons ; the one a practical one, because, if it 

 should be the case, the experimenter would be enabled to exa- 

 mine these currents without such a mass of copper wire and 

 copper ribbon as Henry made use of in his experiments ; the 

 other a theoretical one, it being important to know whether the 

 same differences obtain, between the induced currents of higher 

 orders, as those which have been observed in induced currents of 

 the first order, when the primary current was either that of a 

 galvanic or of an electric battery. 



1. Currents of higher orders when the first induced current is 

 electro-dynamically induced. 



66. The first induced current, which causes the production of 

 currents of higher orders, may either be electro-dynamically in- 

 duced, or it may be a magneto-electric current, and both methods 

 of excitation admit again of several modifications. It is well 

 known that electro-dynamic induction may take place in two 

 ways, either by the approach of a closed wire to, or its removal 

 from a continuous current (as, for instance, the connecting wire of 

 a galvanic or thermo-battery) ; or secondly, when in one of two 

 parallel wires which remain equally distant from each other an 

 electric current is excited or ceases. For the first mode of in- 

 duction the following apparatus may be made use of: — Suppose 

 two circular currents intersecting each other in the manner 

 that two large circles would intersect a ball, they will then tend 

 to cause each other to revolve in one plane, according to the law 



• Transactions of the American Philosophical Society, vol. vi. p. 17. 



