316 LENZ ON THE VARIOUS CONDUCTING POWERS 



Barlow made his experiments in the same manner as Pouillet, and 

 would have obtained the same results had he added, as PouUet did, a 

 constant to the conducting power of his wires, without which his results 

 necessarily proved erroneous. He supposed that the conducting power 

 was inversely as the square root of the length, and directly as the sec- 

 tion. Such a proportion may indeed easily be found between the resist- 

 ance of the pile and the two wires employed for the experiment, that, 

 according to Barlow's calculation, nearly such a law may be obtained. 

 Had he employed, for instance, two wires of the same diameter, the 

 lengths of which were »« and n, his view must have been confirmed, 

 when the conducting resistance of the pile itself was reduced to that of 

 one wire of the same diameter and the length 

 m V(w) — n ^/(m) 



It is indeed not very probable that such would have always been the 

 condition of the pile, but the experiments agree so little with the calcu- 

 lations performed according to his principle, that diiferences of 6° and 

 7° may be found in them. 



Gumming used the thermo-electric pile to excite the current, but he 

 also did not in the least consider the conductibility of the thermo- 

 electric metals ; and he himself owns that the experiments agree but 

 approximately with his theory *. 



We perceive, then, by the above, that all the contradictory results of 

 Barlow's, Cumming'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 performed their 

 experiments. The axiom that the conductibiliti/ of wires of the same 

 substcmce is inversely as their lengths and directly as their sections 

 is established by Ohm and Fechner in so conclusive a manner, and with 

 such a full appreciation of all the connected circumstances, that a 

 further and more minute illustration seems to be almost superfluous ; 

 still the method of determining the power of conductibility by the in- 

 duced electro-dynamic currentf offers so much facility and accuracy 



ratio to the resistance ; and as in the experiment on this subject by Faraday the 

 entire resistance of the voltaic arrangement remained the same, when the wires 

 were compared two by two, the currents produced by induction must also have 

 been the same. 



* [The results obtained by Harris, by means of his thermo-electrometer, 

 (Trans. Royal Soc. of Edin. 1832,) are also easily reconciled with the theory 

 here advocated. This able experimentalist found that the differences in tlie 

 conducting powers of wires of different diameters became more apparent within 

 certain limits, as the force of the battery increased. These experiments were 

 made with wires o" very short lengths and small diameters. — Edit.] 



f Christie has also employed, in his above-mentioned experiments, currents 

 produced by electro-dynamic induction, but more recently than 1 have. His 

 paper was presented to the Royal Society on February the 8th, 1833, whilst 



