462 



Mri Ji P. a oxikt'fi Account of Esoperiments 



^K'^^ 



MBlfe itt^l^^trolniignet^T^. '«: "Weight 1057 M '^t^bW^ 



of coils 7 feet. 



5^wv ^j o\ \0W)$ 



i 



'able III.— Electro-magnet No. 3. Weight 65-3 grs. 

 of coil 1*58 feet. 



Length 



Quantity of cur- 

 rent in degrees. 



0-42 



10 



20 



Electro-mag- 

 netic force. 



0-6G 

 1-58 

 316 



Weight lifted. 



5-5 

 9 

 11 



With great care No. 3 in one instance supported 12 lbs., or 

 1286 times its own weight. 



Electro-magnet No. 4, which weighed only half a grain^ carried 

 in one instance a weight of 1417 grains, or 2834 times its own 

 weight*. There was, however, a good deal of difficulty in expe- 

 rimenting ^vith this minute arrangement, and it is on this account 

 that its greatest lifting power was not observed ; the relative 

 power obtained was nevertheless far greater than any that I had 

 heard of before, and is in fact more tlian eleven times that of the 

 celebrated steel magnet which belonged to Sir Isaac Newton. 



It is well known that the length of a steel magnet ought to 

 bear a great proportion relatively to its breadth and thickness, 

 and that a contrary shape occasions the confusion of the poles, 

 and a general diminution of virtue ; and Dr. Scoresby has found 

 that if a large number of straight steel magnets are bundled 

 together, the power of each is thereby greatly deteriorated. All 

 this is easily understood, and finds its cause in the attempt of 

 each part of the system to induce upon the other part a contrary 

 magnetic polarity to its own. Still there is no reason why the 

 principle of consti-uction should be extended to the electro-mag- 

 net, especially as in its case a great and commanding inductive 

 power is brought into play to sustain what the steel magnet has 

 to support by its own unassisted retentive property. All the 

 preceding experiments confirm this principle ; and I give the 

 following table in proof of its obvious and necessary consequence, 



* I subsequently had the pleasure of presenting Dr. Roget with a still 

 more minute electro-magnet, which had sustained about 3500 times its oyija. 

 weight of iron. — May 1851, J. P. J. 



