220 Mr. Rainey on the Attractive Pomoer of Magnets, 



the latter, may be the prime mover; but that both participate 

 in every galvanic, electro-magnetic, or thermo-magnetic cur- 

 rent. 



XLV. On the Differerice betisoeen the Attractive Poiaersfor soft 

 Iron of the Electro-magnet and the Steel Magnet ,- in reply to 

 Dr. Ritchie. By G. Rainey, Member of the Royal College 

 of Surgeons. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



I'^HE last Number of the Philosophical Magazine, at page 83, 

 contains some remarks by Dr. Ritchie upon a paper which 

 I communicated in May last (printed in the Number for July), 

 concerning the cause of the great disproportion in the attrac- 

 tive power of the electro- magnet for soft iron when in contact 

 and at a distance, compared with the attractive power of the 

 common steel magnet under similar circumstances. The con- 

 cluding paragraph of Dr. Ritchie's paper is as follows : 



" In the explanation given by Mr. Rainey, the lifter is sup- 

 posed to react powerfully on the electro-magnet, so as to in- 

 crease its power, a supposition which cannot possibly be ad- 

 mitted. For the electro-magnet must, in the first place, give 

 the lifter all its magnetic power, consequently the power of the 

 lifter can never exceed that of the electro-magnet, and conse- 

 quently never can induce a higher magnetic state in it than what 

 has already been done by the voltaic helix." What Dr. Ritchie 

 pronounces to be a supposition which cannot possibly be ad- 

 mitted, I will prove, I think to Dr. Ritchie's satisfaction, both 

 by reasoning and experiment, to be an absolute and undeniable 

 fact. My position is, that the lifter of a common horse-shoe 

 magnet can exceed the power of the magnet to which it is ap- 

 plied ; and in case that magnet has not received its maximum 

 of magnetism, can induce in it a higher state of magnetism 

 than that which existed before the application of the lifter; 

 and that in proportion as the permanent magnet resembles in 

 its texture soft iron, the effects of induction on it and on the 

 electro-magnet more closely resemble each other, so as to 

 render it obvious that the effect of the keeper on the two is the 

 same, excepting in degree. 



Let a and b denote the inducing power of the magnet A, and 

 let B be a piece of soft iron, placed in the position represented 

 in the annexed diagram, and sufficiently large to receive all 



