Mr. W. Sturgeon on Electro-Magnets. 1 99 



which it revolves. The direction of motion Is constantly the 

 same whatever may be the nature of the galvanic connec- 

 tions. 



It does not appear that any very extensive experiments were 

 attempted to improve the lifting powers of electro-magnets 

 from the time that my expei'iments were published in the 

 Transactions of the Society of Arts, &c. for 1825, till the latter 

 part of 1828. Mr. Watkins, Philosophical Instrument-maker, 

 Charing Cross, had, however, made them of a much larger 

 size than any which I had employed; but I am not aware to 

 what extent he pursued the experiment. 



In the year 1828 Professor Moll of Utrecht, being on a 

 visit to London, purchased of Mr. Watkins an electro-magnet 

 weighing about five pounds ; at that time I believe the largest 

 which had been made. It was of round iron, about one inch 

 in diameter, and furnished widi a single copper wire twisted 

 round it 83 times. When this magnet was excited by a large 

 galvanic surface, it supported about 75 pounds. 



Professor Moll afterwards prepared another electro-magnet, 

 which when bent was 12^ inches high, 2| inches in diameter, 

 and weighed about 26 pounds ; prepared like the former with 

 a single spiral conducting wire. With an acting galvanic sur- 

 face of 1 1 square feet, this magnet would support 154 pounds, 

 but would not lift an anvil which weighed 200 pounds. 



The success of these experiments, which established the first 

 grand step in exalting the attractive powers of electro-magnets, 

 gave anew impulse to the inquiry, which the American philoso- 

 phers have pursued to an extent that will not be very easily sur- 

 passed. By dividing about 800 feet of conducting wire into 26 

 strands, and forming it into as many separate coils round a bar 

 of soft iron about 60 pounds in weight, and properly bent into 

 the horse-shoe form. Professor Henry has been enabled to pro- 

 duce a magnetic force which completely eclipses every other 

 in the whole annals of magnetism ; and no parallel is to be 

 found since the miraculous suspension of the celebrated Orien- 

 tal impostor in his iron coffin *. 



This electro-magnet is said to have supported nearly two 

 tons when excited by about five S(juare feet of galvanic surface, 

 an extent comparatively trifling, when compared to the pro- 

 digious magnetic force which it is capable of calling into 

 action. 



The largest electro-magnet which I have as yet exhibited 

 in my lectures weighs about 16 pounds. It is formed of a 

 square bar of soft iron, \h inch across each side: the poles 



* Siliiman's Journal. 



are 



