for determining the conducting Power of Wires. 1 1 



lates to diameter, and another nearly as large between the 

 conducting power of different metals as given by various au- 

 thors, including men of the first rank in the science, we must 

 conclude that there is some inaccuracy, and that there are pro- 

 bably other circumstances influencing the results which are not 

 at present understood. If the explanation I have attempted 

 should be thought satisfactory I shall feel much gratified ; and 

 if not, and it should only lead to inquiries that shall elicit a 

 satisfactory explanation, my object will have been attained. 



P.S. My attention during the last three or four years hav- 

 ing been withdrawn from electro-magnetic experiments, I was 

 not aware till this paper had been set up that the subject of 

 these discrepancies had been so fully investigated by M. Lenz, 

 in an article in Taylor's Scientific Memoirs, Part II. p. 311. 

 The paper, as I have stated, was written in 1834-, and my at- 

 tention was only recalled to it by an accidental conversation 

 with a foreigner, to whom, it would appear, Lenz's Memoir was 

 equally unknown *. 



* [The paper by Lenz here referred to by Mr. Barlow is entitled * On 

 the Laws of the Conducting Powers of Wires of different Lengths and Diame- 

 ters for Electricity." In it are successively reviewed the researches and 

 reasoning on the subject, of Ritchie, Davy, Becquerel, Pouillet, Barlow, 

 dimming, and Christie; together with a formula derived from the theory 

 of the galvanic battery by Ohm, which theory, M. Lenz remarks, " being 

 only published in German, it is unknown both in France and in England." 

 " This theory," however, he states, " explains perfectly the difference 

 between Barlow's results and those of other natural philosophers who have 

 occupied themselves with this subject, as well as the doubts of Ritchie." 

 After his examination of the results obtained by the physicists above men- 

 tioned M. Lenz observes, " We perceive, then, by the above, that all the 

 contradictory results of Barlow's, dimming' s, and Ritchie's experiments, in 

 opposition to the law established by other philosophers, are reduced to a 

 mere nothing by an accurate appreciation of the mode in which they per- 

 formed their experiments ;" and he states that " the axiom that the con- 

 ductibility of wires of the same substance is inversely as their lengths and di- 

 rectly as their sections" has been conclusively established by Ohm and 

 Fechner. He then describes the results which he has himself obtained by 

 the induced electro-dynamic current, and which are entirely in agreement 

 with that axiom. The proposition " that in equally good conducting wires 

 of the same substance the lengths are proportional to the masses, that is to 

 say, to the sections," appears, it may be added, to have been first demon- 

 strated by Davy. No. IV. of Scientific Memoirs, to be published this 

 month, will contain another paper by Lenz, On the laws according to 

 which the magnet acts on a spiral, and on the influence of the distance of 

 the convolutions of spirals on the production of the electromotive power 

 in them. — Edit.] 



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