124 On certain Properties of Common and Electro-Magnets, 



power of an electro-magnet to communicate permanent mag- 

 netism, even with the very long magnet which I have employed, 

 is much inferior to that of a permanent magnet possessing the 

 same lifting power. Hence, to magnetize to saturation it will 

 be useful to employ a very long electro-magnet. 



Having thus reduced these curious facts to a general prin- 

 ciple, I have taken the liberty of requesting you to give them 

 a place in the Philosophical Magazine. 



I am, dear Sir, yours truly, 

 University of London, July 18, 1833. William RlTCHlE. 



XXVI. On certain curious Properties of Common and Electro- 

 Magnets, By the Rev. William Ritchie, LL.D. F.R.S. 



Professor of Natural Philosophy in the Royal Institution of 

 Great Britain and in the University of London. 



To Richard Taylor •, Esq. 

 Dear Sir, 



TN a series of experiments which were read at a meeting of 

 -*- the Royal Society some time ago, I stated that when an 

 electro-magnet had the magnetic state induced on it by re- 

 maining in contact with the battery for some time, it required 

 a considerable time to induce an equal magnetic power by 

 changing its poles ; but that the same power was again ra- 

 pidly restored, by inducing the poles at the same extremities 

 as at first. The success of the experiment depends much on 

 the length of the soft iron horse-shoe magnet, and on the 

 weakness of the battery. To render the effect very striking, 

 a long magnet and a weak voltaic power are conditions abso- 

 lutely necessary. But the property does not only belong to 

 an electro-magnet, but in a more striking degree to a per- 

 manent magnet of hard steel. If a horse-shoe of tempered 

 steel be magnetized in the usual way and allowed to remain 

 for some time (the longer the better), and if its magnetism be 

 completely destroyed by an opposite touch, it will be found 

 exceedingly difficult to communicate magnetism to it by re- 

 versing the poles. If after repeated touches a small power 

 should be induced, it will not only be destroyed by a single 

 touch of the same magnet, but will even have its poles re- 

 versed. If the operation be continued even for a considerable 

 length of time, by successively changing the poles, it will still 

 be found that it will be magnetized much more rapidly in the 

 direction in which it was originally magnetized than in the 

 contrary. 



