262 BULLETIN OP THE 



Engineering, Henry gave by request an account of the great 

 extension of the Railway and Canal systems in the United States : 

 which was listened to with great attention and interest. He also 

 referred to the inland or river navigation in our country, 

 describing the improvements introduced into our large river 

 steam-boats, especially on the Hudson river in New York State ; 

 where the usual speed was fifteen miles per hour or more.* 



In November, 1837, Henry returned from his foreign tour 

 greatly invigorated, — bringing with him some new apparatus: 

 and with increased zest he re-embarked upon the duties of his 

 professorship. Continuing his studies of electrical action, he 

 presented verbally to the American Philosophical Society, Feb- 

 ruary 16th 1838, a notice of further observations on the "lateral 

 discliarge" of electricity while passing along a wire, going to 

 show that even with good earth connection, iree electricity is not 

 conducted silently to the ground. f 



In May, 1838, he announced to the Society the production of 

 currents by induction from ordinary or mechanical electricity, 

 analogous to that first obtained by Faraday from galvanism in 

 1831 : and the further curious fact that on the discharge from a 

 Leyden jar through a good conductor, a secondary shock from a 

 perfectly insulated near conductor could be obtained more intense 

 than the primary shock directly from the jar.| 



These investigations having in view the discovery of "induc- 

 tive actions in common electricity analogous to those found in 

 galvanism" (commenced in the Spring of 1836), led to renewed 

 examination of the secondary galvanic current, which since No- 

 vember 24th, 1831, (or for seven years,) had received no special 

 attention. Henry's very interesting series of experiments were 

 detailed in a somewhat elaborate memoir read before the Ameri- 

 can Philosophical Society, November 2nd, 1838. Employing 

 five different sized annular spools of fine wire (about one-Iiftieth 

 of an inch thick) varying from one-fifth of a mile to nearly a 

 mile in length (which might be called "intensity" helices) ; and 

 six flat spiral coils of copper ribbon varying from three-quarters 

 of an inch to one inch and a half in width, and from 60 to 93 

 feet in length (which might be called "quantity" coils), he was 

 able to combine them in various ways both in connection and in 

 parallelism. A cylindrical battery of one and three quarters square 



*Sanie Report, Abstracts, p. 135. It was on this occa.«ion that Dr. 

 Lardner, generalizing probablv from his observation.s on the Thames, 

 ventured (not verv conrteously) to .ionbt whether any such speed as fif- 

 teen miles per hour on water, could ordinarily be effected. (Sill. Am. 

 Jour. Sci. Jan. 1838, vol. xxxii. p. 296.) The same authority affirmed 

 the futility of attemptinsr oceanic steam navigation. 



t Prorep.flin,i!i Am. Phil. Sor. Feb. 16, 1838, vol. i. p. 6. 



t Proceedings Am. Phil. Soc. May 4, 1838, vol. i. p. 14. 



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