246 MEMORIAL, OF JOSEPH HENRY. 



exposed wires become luminous : and " when the wire is formed into 

 a flat spiral, the outer spiral alone exhibits the lateral discharge, but 

 the light in this case is very brilliant: the inner spirals appear to 

 increase the effect by induction." In like manner when a ball was 

 attached to the middle of a vertical lightning-rod having a good 

 earth-connection, "when sparks of about an inch and a half were 

 thrown on the ball, corresponding lateral sparks could be drawn 

 not only from the parts of the rod between the ground and the ball, 

 but from the part above, even to the top of the rod." * 



At the same meeting, before the section on Mechanics and Engi- 

 neering, 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 im- 

 provements introduced into our large river steamboats, especially on 

 the Hudson river in New York State; where the usual speed was 

 fifteen miles per hour or more, f 



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 pro- 

 fessorship. Continuing his studies of electrical action, he presented 

 verbally to the American Philosophical Society, February 16th, 

 1838, a notice of further observations on the "lateral discharge" 

 of electricity while passing along a wire, going to show that even 

 with good earth connection, free electricity is not conducted silently 

 to the ground. J 



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 



* Report of Brit. Association, for 1837, pp. 22-24, of Abstracts. 



t Same Report, Abstracts, p. 135. It was on this occasion that Dr. LARDNER, gen- 

 eralizing probably from his observations on the Thames, ventured (not very courte- 

 ously) to doubt whether any such speed as fifteen miles per hour on water, could 

 ordinarily be effected. (Sill. Am. Jour. tiei. Jan. 1838, vol. xxxiii. p. 296.) The same 

 authority affirmed the futility of attempting oceanic steam navigation. 



^Proceedings Am. Phil. Soc. Feb. 16, 1838, vol. i. p. 6. 



