240 BULLETIN OF THE 



plates, the horse-shoe became much move powerfully magnetic 

 than another of the same size (and wound in the usual manner) 

 by the application of a battery composed of 28 plates of copper 

 and zinc each 8 inches square." In this case the coil was wound 

 upon itself. 



Henry^s "Quantify" Magnet compared with IIoWs. — Shortly 

 after this, Dr. G. Moll, (Professor of jS'atural Philosophy in 

 the University of Utrecht,) having seen in England, in 1828, 

 an electro-magnet of Sturgeon's which supported nine pounds 

 from its armature, " determined to try the effect of a larger 

 galvanic apparatus ;" and in a paper published in 1830,* re- 

 marks : "I obtained results which appear astonishing, and are — 

 as far as the intensity of magnetic force is concerned, altogether 

 new. I have anxiously looked since that time into different 

 scientific continental and English journals, without finding any 

 further attempt to extend and improve Mr. Sturgeon's original 

 experiment." Moll's horse-shoe formed of a round bar of iron 

 about 1 inch thick, was about 8^ inches in height, and had a 

 wrapped copper wire of about one-eighth inch diameter coiled 

 83 times around it. The weight of the horse-shoe and wire was 

 about 5 pounds ; of the armature, about 1^ pound ; and with a 

 single galvanic pair whose acting zinc surface was about 11 

 square feet, the electro-magnet supported about 50 pounds. With 

 cautious additions, the load could be increased to 75 pounds. 

 An additional galvanic pair of about 6 square feet was applied 

 without increasing the power of the magnet.f 



As soon as the account of Moll's magnet reached this country, 

 Henry who had obtained and had publicly exhibited nearly two 

 years previously, considerably higher results, and who realized 

 that there was at least one very important difference of construc- 

 tion Ijetween his own magnet and that of the Dutch savant, felt 

 it a duty at once to publish the details of his own researches, in 

 a more public form : — which he accordingly did in the January 

 number of Silliraan's American Journal of Science for 1831 ; 

 (then published only quarterly ;) causing a copy of Professor 

 Moll's paper, taken from Brewster's Edinburgh Joui'nal of 

 Science for October 1830, to be inserted in the same number. 

 At the conclusion of his own article he remarks : " The only 

 effect Professor Moll's paper has had over these investigations, 

 has been to hasten their publication : the principle on which 

 they were instituted was known to us nearly two 3''ears since, 

 and at that time exhibited to the Albany Institute." 



The magnet which he had subsequently made, consisted of a 

 cylindrical bar of iron one-half inch in diameter and about 10 

 inches long, bent into a horse-shoe and closely wound with several 



* Bihiinthhque Uvirergelle, 1830, cah. 45, p. 19. 



t tirewster'rf Edinburgh Jour. Set Oct. 1830, vol. iii. n. s. pp. 209-218. 



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