THE 



LONDON AND EDINBURGH 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



AUGUST 1836-. 



XVI. On the Cause of the remarkable Difference hettsoeen the 

 Attractions of a Permanent and of an Electro-Magnet on Soft 

 Iron at a Distance. By the iZ^t'. William Ritchie, Z/Z/.Z)., 

 F.R.S., Professor q/' Natural Philosophy in the Royal Institu- 

 tion and in the University of London.^- 



A S soon as the electro-magnet was constructed and em- 

 "^^ ployed to illustrate the immense magnetic power com- 

 municated to soft iron, it must have been observed that its at- 

 traction for iron filings or pieces of soft iron at a distance was 

 much less than that of a permanent magnet of equal lifting 

 power. This peculiar properly rendered the electro-magnet 

 not well suited for magnetic induction at a distance ; and hence, 

 after a few unsuccessful trials to substitute it for the perma- 

 nent magnet in my apparatus for continued rotation, it was 

 long since abandoned. In a short paper by Mr, Ilainey in the 

 last Number of this Journal, p. 72, the fact is stated, and an 

 explanation attempted to be given of this peculiarity; but I am 

 afraid the explanation will not be found in accordance with 

 the present state of the science. This subject having en- 

 gaged my attention some years ago, I had seveial times com- 

 menced a paper intended for the Philosophical Magazine, but 

 other more pressing subjects prevented me from linishiu"- it. 

 As the fact is a necessary consequence of the properties of 



• Communicated by the Author. 

 Third Sates. Vol.9. No. 52. Aug. 18.%. K- 



