PHILOSOPHICAL SOCIETY OF WASHINGTON. 211 



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 cur- 

 rent 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 jS'assau Hall : the secondary or induction wire 

 being suspended in a parallel direction across the grounds at the 

 rear of JS'assau 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 

 recotidite 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 elec- 

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

 tended to strengthen the hypothesis of an a^therial dymimic 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 in- 

 quiries undertaken by Henry in various fields, it is necessary to 

 pause here, and to recur to some of his earlier scientific labors. 



Meteorology. — From an early date Henry took a deep interest 

 in tlie study of meteorology : not only on account of its practical 

 importance, but from its relation to cosmical physics, and because 

 from the very complexity and irregularity of its conditions, it 

 challenged further investigation and stood in need of larger gene- 

 ralizations. His early nssociation with Dr. T. Romeyn Beck in 

 the first development of the system of meteorological observations 

 established in the State of New York, has already been referred 

 to in the sketch of his "Early Career." This actiive and zealous 

 co-operation continued from 1827 to J 832; or as long as he re- 

 sided in Albany. 



In September of 1830, he commenced a series of observations 

 for Professor Renwick of Columbia College, to determine the 

 magnetic intensity at Albany. With the assistance of his 

 brother-in-law, Professor Stephen Alexander, these observations 



* ProrePdinqs Am. Phil. So". Oct 21, 1842, vol. ii. p. 229. 



t In a paper "On tlie Theory of tlie so-called ImpotiHer;ibles" published 

 some years later, in referring to the plienotnena of electrifal o.«cillati(in in 

 discharsze, and of the series of inductions takine place and "extendiiiu to 

 a surprising distance on all sides," he remarks: "As tliese are the lesult* 

 of currents in alternate directions, they :nnst produce in surrounding 

 space a series of pi un and minus motions, analogous to — if not identical with 

 uudulations." {Proceed. Amer. Association, Albany, Aug. 1851, p. 89.) 



28 



