Prof. Henry's ContriJmtio7is to Electricity a7id Mag?ietism. 551 



tion lias already given rise to so many errors ; further, the resistance of oppo- 

 sition, an element hitherto little attended to in England*, which is not merely in 

 itself of importance, but to which especial regard must be had in the discussion 

 of the two views respecting the origin oi voltaic electricity, as it is considerably 

 affected by the chemical action. Very generally the heightening of the inteu- 

 sit}' of the current by direct chemical attack on the one or other metal of the 

 circuit is merely due to the diminution of the resistance of transition, and is not 

 a result of the increase of the electromotive force. But it must be proved with 

 respect to this force, that it is in direct ratio to the energy of the chemical action 

 on one of the metals (or to the difference of the actions on both metals) of the 

 circuit, if the chemical theory is to be regarded as founded. It would, however, 

 then be requisite to continue to separate and quantitatively to determine the in- 

 dividual elements which have any influence on the intensity of the current, in the 

 same way as it has been done by Fechner in his work, " Mnas hestimrmmgen 

 iiber die Galvanische Kette (Leipzic, 1831, 260 pages in quarto). I am con- 

 vinced that the English physicists, to whose zeal and ability we are already in- 

 debted for so many interesting facts in the field of galvanism, would add con- 

 siderably to the extension of our scientific knowledge of this branch of physics, 

 and would consider Fechner's memoir on the Con tact- theoryf in a different 

 point of view were they more intimately acquainted with that work, based on 

 Ohm's theory, and illustrating and extending it. 



POGGENDORFF. 



* By which, among other things, the recent, important, and interesting dis- 

 covery of Mr. Roberts (See L. & E. Phil. Mag. for Feb.) finds its explanation. 



f Besides the article on the Contact-theory, translated in the Phil, Mag., 

 might be mentioned two others in Poggendorff's Annalen, vol. xlv. p. 432, and 

 vol. xlix. p. 433. What Schcenbein has brought forward against it does not 

 appear to me to have any weight, and indicates his non-acquaintance with 

 Ohm's theorv. 



LX XXIV. Contributio7is toElectricity and Magnetism. No. III. 

 On Electro- dynamic Induction. By Joseph Henry, LL.D., 

 Prof, of Natural Philosophy in the College of Neiso Jersey, 

 Princeto7i. 



[Continued from p. 265, and concluded.] 



Section VI. — The production of induced Curre7its of the dif- 

 ferent Orders from ordinary Electricity. 



98. r|R« FARADAY, in the Ninth Series of his Researches, 

 -^-^ remarks, that " the effect produced at the commence- 

 ment and the end of a current (which are separated bj^ an in- 

 terval of time when that current is suppHed from a voltaic 

 apparatus) must occur at the same moment when a common 

 electrical discharge is passed through a long wire. Whether 

 if it happen accurately at the same moment they would entirely 

 neutralize each other, or whether they would not still give some 

 definite peculiarity to the discharge, is a matter remaining to 

 be examined." 



99. The discovery of the fact, that the secondary current, 

 which exists but for a moment, could induce another current 



