^ DISCOURSE OF W. B. TAYLOR. 257 



discovered the very simple solution, by a reference to the self-induc- 

 tion of the rod, a negative wave passing, succeeded immediately 

 by a positive wave so rapidly as to completely neutralize the eifect 

 upon the electroscope before the inertia of the gold-leaf could be 

 overcome, while actually producing a double spark (sensibly co-in- 

 cident) to and from the recipient. 



A few months later, "he had succeeded in magnetizing needles by 

 the secondary current, in a wire more than two hundred and twenty 

 feet distant from the wire through which the primary current was 

 passing, excited by a single spark from an electrical machine."* 

 In this case the primary wire was his telegraph line stretched seven 

 years before across the campus of the college grounds in front of 

 Nassau Hall; the secondary or induction wire being suspended in 

 a parallel direction across the grounds at the rear of Nassau Hall, 

 with its ends terminating in buried metallic plates: the large 

 building intervening between the two wires. 



This brilliant series of contributions to our knowledge of a most 

 recondite and mysterious agent, placed Henry, by the concurrent 

 judgment of all competent physicists, in the very front rank of 

 original investigators.- His persevering researches in the electrical 

 paradoxes of induction, perhaps more than any similar ones, tended 

 to strengthen the hypothesis of an setherial dynamic agency; although 

 he himself had for a long time been inclined to favor the material 

 hypothesis, f 



INVESTIGATIONS IN GENERAL PHYSICS: FROM 1830 TO 1846. 



In order to give a proper connection to the experimental inqui- 

 ries undertaken by Henry in various fields, it is necessary to pause 

 here, and to recur to some of his earlier scientific labors, begin- 

 ning again at Albany. 



* Proceedings Am. Phil. Soc. Oct. 21, 1842, vol. ii. p. 229. It is barely possible that 

 the primary current might have returned through the second wire. 



fin a paper "On the Theory of the so-called Imponderables" published some 

 years later, in referring to the phenomena of electrical oscillation in discharge, and 

 of the series of inductions taking place and " extending to a surprising distance on 

 all sides," We remarks : "As these are the results of currents in alternate directions, 

 they must produce in surrounding space a series of plus and minus motions, anal- 

 ogous to if not identical with undulations." (Proceed. Amer. Association, Albany, 

 Aug.lSol, p. 89.) 



17 



