1837] WEITINGS OF JOSEPH HENRY. 101 



NOTICE OF ELECTRICAL RESEARCHES — THE LATERAL 



DISCHARGE. 



(Keport of British Association, 1837, vol. vi, part ii, pp. 22-24.)* 



September, 1837. 



The primary object of these investigations was to detect, 

 if possible, an inductive action in common electricity anal- 

 ogous to that discovered in a current of galvanism. For 

 this purpose an analysis was instituted of the phenomena 

 known in ordinary electricity by the name of the lateral 

 discharge. Professor Henry was induced to commence with 

 this from some remarks by Dr. Roget on the subject. The 

 method of studying the lateral spark consisted in catching 

 it on the knob of a small Leyden phial, and presenting this 

 to an electrometer. The result of the analysis was in ac- 

 cordance with an opinion of Biot that the lateral discharge 

 is due onl}^ to the escape of the small quantity of redundant 

 electricity which always exists on one or the other side of a 

 jar, and not to the whole discharge. The Professor then 

 stated several consequences which would flow from this, 

 namely, that we could increase or diminish the lateral action 

 by the several means which would affect the quantity of 

 redundant or as it may be called free electricity, such as 

 an increase of the thickness of the glass, or by substituting 

 for the small knob of the jar a large ball. But the arrange- 

 ment 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 beautifull}^ 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. 

 In this arrangement the electricity of the globe may be con- 

 sidered nearly all as free electricity; and as the insulated 



* [Re-printed in Silliraan's American Journal of Science, April, 1838, pp 

 16-18.] 



