200 WRITINGS OF JOSEPH HENRY. [1842 



CONTRIBUTIONS TO ELECTRICITY AND MAGNETISM. No. V. 



ON INDUCTION FROM ORDINARY ELECTRICITY; AND ON THE 

 OSCILLATORY DISCHARGE.* 



(Proceedings of the American Philosophical Society, vol. ii, pp. 193-196.) 



June 17, 1842. 



Professor Henry presented the record of a series of experi- 

 ments on induction from ordinary electricity, as the fifth 

 number of his Contributions to Electricity and Magnetism. 

 Of these experiments he gave an oral account, of which 

 the following is the substance. 



In the third number of his Contributions he had shown 

 on this subject: 1. That the discharge of a Leyden battery 

 through a conductor, developed in an adjoining parallel 

 conductor an induced current, analogous to that which, 

 under similar circumstances, is produced by a galvanic cur- 

 rent. 2. That the direction of the induced current, as indi- 

 cated by the polarit}^ given to a steel needle, changes its sign 

 with a change of distance of the two conductors, and also 

 with a change in the quantity of the discharge of elec- 

 tricity. 3. That when the induced current is made to act 

 on a third conductor, a second induced current is developed, 

 which can again develop another, and so on through a series 

 of successive inductions. 4. That when a plate of metal is 

 interposed between any two of the consecutive conductors, 

 the induced current is neutralized by the adverse action of 

 a current in the plate. 



The direction of the induced currents in all the author's 

 experiments was indicated by the polarity given to steel 

 needles enclosed in a spiral, the wire of which formed a part 

 of the circuit. But some doubts were reasonably entertained 

 of the true indications of the direction of a current by this 

 means, since M. Savary had announced in 1826, that when 

 several needles are placed at different distances above a 



* [The full Memoir was not printed in the "Transactions of the Am. Philo- 

 sophical Society."] 



