216 WRITINGS OP JOSEPH HENRY. [1843 



Theory of the discharge of the Leyden jar. 



Referring to the theory of the discharge of the Leyden jar, 

 which he had submitted to the Society some time since,* 

 Professor Henry examined some apparent objections to it, 

 resulting from the researches of Matteucci. The effect pro- 

 duced on the galvanometer by the discharge of a battery is 

 due to the retardation of the lesser waves of electricity, a fact 

 which indicates the cause of Matteucci's results, when a card 

 was pierced by the currents induced in a neighboring wire 

 conductor forming an open circuit. 



The speaker described several experiments on the direct 

 and return stroke, showing that equilibrium was restored 

 by the same succession of oscillations; large and small 

 needles placed in spirals forming part of an electrical circuit, 

 being magnetized in different directions. The disturbance of 

 the electrical plenum by a discharge of electricity was referred 

 to as explanatory of the induction which takes place, and 

 the subject was applied to the explanation of various phe- 

 nomena; among others, the light appearing in well authen- 

 ticated cases about persons and objects in the neighborhood 

 of a discharge of lightning in its direct passage, and sugges- 

 tions were made as to the most effectual mode of protecting 

 powder houses, etc., from the effects of lightning. 



Professor Henry examined in the same connection whether 

 currents or ordinary electricity pass actually at the surface, 

 or like galvanic electricity, through the mass of the conductor, 

 and he concluded that the law of conduction developed by 

 Ohm cannot apply to the case of surface passages, as these 

 are indicative of ordinary electricity. 



* Contributions No. V, June 17, 1842. 



