THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



DECEMBER 1886. 



LVII. Notes on Electricity and Magnetism. — II. The Self- 

 induction and Resistance of Compound Conductors. By 

 Lord Raylbigh, Sec. R.S., D.C.L.* 



BEFORE entering upon the proper subject of this com- 

 munication, I take the earliest opportunity of correcting 

 a mistake of some importance into which I fell in connection 

 with induction-coils. From the fact that a closed magnetic 

 circuit acts very ill as a store of energy, I argued that closed 

 electromagnets were to be condemned as secondary generators 

 (Phil. Mag. August 1886, p. 179). Dr. Hopkinson and Prof. 

 Ewing have independently drawn my attention to the fact 

 that the success of induction-coils does not depend upon 

 storage of energy, and that they might work with high effi- 

 ciency even though the whole of the energy put into the iron 

 were wasted. Prof. E wing's remark, to which I took excep- 

 tion, is thus perfectly correct. 



In his inaugural address to the Society of Telegraph Engi- 

 neers!, and in a subsequent communication to the Royal 

 Society J, Prof. Hughes has described a series of interesting 

 experiments, which have attracted a good deal of attention 

 in consequence both of the official position and known expe- 

 rimental skill of the author. Some of the conclusions which 

 he advances can hardly be sustained, and have met with severe 

 criticism at the hands of Weber, Heaviside, and others. There 



* Communicated by the Author. 



t Joiirn. Tel. Eng. vol. xv. (1866) p. I. 



X Proc. Roy. Soc. vol. xl. (1886) p. 461. 



Phil. Mag. S. 5. Vol. 22. No. 139. Dec. 1886. 2 K 



