PIIILOSOPIITCAL SOCIETY OF AVASIIINOTON. 201 



magnetic circuits, experimentally tried more than a year jire- 

 viously. 



Nearly a year was employed in foreifi'ii travel, most jileasantly 

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

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

 Henry formed the acipiaintance of Arago, Jieecpierel, I)e la 

 Rive, Biot, Gay-Lussae, and other celebrities,) and in Kdiii- 

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

 minds. 



In September of the same year (1837) ho attended the meet- 

 ing of the British Association at I^iverpool ; 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 l)y some remarks 

 of Dr. Koget 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." Hence we could 

 increase or diminish tin; lat(!ral action by any means which affect 

 the quantity of free electricity: — as by "an increas(! 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 (aid by a small 

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

 foot in diameter, the wire at each discharge beef)mes beautifully 

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

 long : rays arc given off on all sides perpcndictdar to the axis of 

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

 stated "that the same (pianlity of electricity could be made to 

 remain on the wire, if grndually 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 moment um. When 

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

 connection), only the outer sides of the exposed wires become 

 luminous: atul "when the wire is formed into n flat spiral, the 

 outer spiral alone exliibits the lafernl disehnrge, but the light in 

 this case is very brilliant : the inner s])irals 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 spnrks of nbout an inch and a hnlf were 

 thrown on the ball, corresponding lateral sytarks 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 



* Re/>nrt nf Brit. Association, for 1837, pp. 22-24, of Abstracts. 



35 



