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XIII. — Eoqjerimental Researches on the Lifting Power of the Electro-Magnet. 

 Part I. By the Rev. T. R. Robinson, D. D., Member of the Royal Irish 

 Academy, and of other Scientific Societies. 



Read June 14, 1852. 



As soon as Oersted's great discovery had led to the construction of electro- 

 magnets, high expectations were formed that they might afford a motive power 

 as energetic and more economical than the steam-engine. The prodigious force 

 wliich they manifest when excited by even a feeble current, and the power of 

 annulling or reversing it in an instant, might seem to justify the hope; and an 

 immense amount of inventive talent has been expended in attempts to realize it. 

 These attempts, however, have shown that electro-magnetic engines can scarcely 

 ever be either a cheap or a very efficient source of power. Electricity is now 

 known to have a definite mechanical equivalent ; the zinc and acids required 

 to produce it are more costly than the coal, which will evolve isodynamic heat ; 

 and the hitherto contrived methods of converting electro-magnetism into moving 

 force involve much more loss than the mechanism of the steam-engine does in 

 respect of heat. I may add, that the great magnetic force which I have referred 

 to exists only in contact ; on the least separation of the keeper it decreases ra- 

 pidly, not merely because magnetic force follows the law of the inverse square 

 of the distance, but because that separation destroys in a very great degree the 

 actual magnetism of the magnet. It must, however, be kept in mind that there 

 are many cases where economy and intensity are of less consequence than faci- 

 lity of application and convenience ; in which, therefore, the electro-magnetic 

 engine deserves a preference even for industrial purposes, and much more for 

 the work of the experimental physicist, although its action may be more costly. 

 In particular, the absence of all danger, and perfect quiescence when not put in 

 VOL. xxn. 2 Q 



