T II U 



LONDON and EDINBURGH 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



JULY 1837. 



I. On the Electro-magnetic conducting Power of Wires of 

 different Qualities and Dimensions, and an Inquiry into the 

 Efficiency of the Galvanometer for determining the Laws of 

 its Variation. By Peter Barlow, F.R.S., Cor. Mem. List. 

 France, fyc. tyc* 



TN the Bakerian Lecture for 1833f, Mr. Christie has given 

 A the details of a long and interesting series of experiments 

 on the magneto-electric conducting power of wires of different 

 lengths and diameters; from the results of which he infers 

 that the law of conduction in this case is, that it varies di- 

 rectly as the square of the diameter, and inversely as the 

 length of the wire ; and in a subsequent part of the same arti- 

 cle, by a comparison of the experiments of different authors, 

 he infers that the same law has place in electro-magnetic con- 

 duction J, My object in this paper is, to explain the anomalies 

 that have been observed, and to inquire whether the deflections 

 produced by the galvanometer ought to be considered as pro- 

 per measures of the conducting power of the wire without re- 

 ference to the power of the battery. 



It is very desirable that we should be able to reduce the 

 laws of electro-magnetic action to mathematical principles, 

 and at a very early stage in the progress of this science I un- 



* Communicated by the Author. 



t This paper was written in 1834, with an intention of publishing it at 

 that time j it has however been lying in my drawer ever since, and as the 

 subject is again brought forward, it may not, perhaps, be uninteresting to 

 some of the readers of the Philosophical Magazine. 



1 [An abstract of Mr. Christie's Bakerian Lecture will be found in Lond. 

 and Edinb. Phil. Mag. vol. iii. p. 141, and some remarks upon it by Dr. 

 Ritchie, in vol. iv. p. 208. — Edit.] 



Third Series. Vol. 1 1 . No. 64. July 1837. B 



