1838] WRITINGS OF JOSEPH HENRY. 107 



current is separately examined, and its direction found to 

 be the same as that of the battery current- The question is 

 then raised, how two currents in the same direction can 

 counteract each other? An answer to this question is given 

 in a subsequent part of the paper. 



The fourth section relates to the discovery of induced 

 currents of the third, fourth, and fifth orders; that is, to the 

 fact that the second current is found capable of inducing a 

 third current, and this latter again another, and so on. The 

 properties of these new currents are next examined, and the 

 screening influence is found to take place between them; 

 quantity is induced from intensity, and conversely; magne- 

 tism is developed in soft iron, decomposition is effected, and 

 intense shocks are obtained, even from the current of the 

 fourth order. A remarkable and important fact is stated in 

 reference to the direction of these currents. If the direction 

 of the battery current and that of the second be called plus, 

 then the direction of the third current will be minus,' oi 

 the fourth current plus, of the fifth minus, and so on. The 

 application of the fact of these alternations is made to the 

 explanation of the phenomenon of screening before men- 

 tioned, and also to the improvement of the magneto-electri- 

 cal machine. 



The last part of the paper relates to the discovery of 

 secondary currents, and of currents of the several orders, in 

 the discharge of ordinary electricity. Shocks are obtained 

 from these, the screening influence of good conductors is 

 shown to take place, magnetism is developed, and the alter- 

 nations in the direction are found to exist as in the cur- 

 rents from galvanic induction. Some remarkable results are 

 given in reference to the great distance at which the induc- 

 tion takes place. Experiments are detailed in which needles 

 were made magnetic when the conductors were removed to 

 the distance of twelve feet from each other. 



Prof. Henry made a verbal communication during the 

 course of which he illustrated experimentally the pheno- 

 mena developed in his paper. 



