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 effect 

 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," he 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. 18ol, p. 89.) 



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