PHILOSOPHICAL SOCIETY OP WASHINGTON. 261 



magnetic circuits, experimentally tried more than a year pre- 

 viously. 



]SJ early a year was employed in foreign travel, most pleasantly 

 and beneficially both for mind and body : the greater portion of 

 the time however being spent in London, in Paris, (where 

 Henry formed the acquaintance of Arago, Becquerel, De la 

 Kive, Biot, Gay-Lussac, and other celebrities,) and in Edin- 

 burgh, where he also found a galaxy of eminent and congenial 

 minds. 



In September of the same year (183*7) he attended the meet- 

 ing of the British Association at Liverpool ; where being invited 

 to speak, he made a brief communication on some electrical 

 researches in regard to the phenomenon known as the " lateral 

 discharge:" — a study to which he had been led by some remarks 

 of Dr. Roget on the subject. " The result of the analysis was 

 in accordance with an opinion of Biot — that the lateral dis- 

 charge is due only to the escape of the small quantity of 

 redundant electricity which always exists on one side or the 

 other of ajar, and not the whole discharge." H'ence we could 

 increase or diminish the lateral action by any means which affect 

 the quantity of free electricity: — as by "an increase of the 

 thickness of the glass, or by substituting for the small knob of 

 the jar, a large ball. But the arrangement which produces the 

 greatest effect is that of a long fine copper wire insulated, — 

 parallel to the horizon, and terminated at each end by a small 

 ball. When sparks are thrown on this from a globe of about a 

 foot in diameter, the wire at each discharge becomes beautifully 

 luminous from one end to the other, even if it be a hundred feet 

 long : rays are given off on all sides perpendicular to the axis of 

 the wire:" — forming a continuous electrical brush. It was also 

 stated " that the same quantity of electricity could be made to 

 remain on the wire, if gradually communicated [by a point] ; but 

 when thrown on in the form of a spark, it is dissipated as before 

 described :" — as though possessing a kind of momentum. When 

 two or more wires are arranged in parallel lines (in electrical 

 connection), only the outer sides of the 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 havino: 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 



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



35 



