124 ^^^ Smithsonian Institution 



pounds. These improvements rendered possible not only his 

 own subsequent discoveries, but also those of Faraday, which 

 began first to assume importance after the invention of 

 Henry's magnets. 



The quantity magnet perfected by Henry in 1830 was the 

 means by which both he and Faraday discovered magneto- 

 electricity. It has been used in almost all electrical work, 

 scientific or practical, which has since been attempted. Stur- 

 geon wrote in 1832 : " Henry has been enabled to produce 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 Oriental 

 impostor in his iron coffin."^ 



"The importance of this discovery," wrote Professor Wil- 

 liam B. Taylor of the intensity magnet, " can hardly be over- 

 estimated. The magnetic 'spool' of fine wire — of a length 

 tens and even hundreds of times that ever before employed 

 for this purpose — was in itself a gift to science, which really 

 forms an epoch in the history of electro-magnetism. It is 

 not too much to say that almost every advancement which 

 has been made in this fruitful branch of physics since the time 

 of Sturgeon's happy improvement, from the earliest researches 

 of Faraday downward, has been directly indebted to Henry's 

 magnets. By means of the Henry ' spool ' the magnet almost 

 at a bound was developed from a feeble childhood to a vigor- 

 ous manhood. And so rapidly and generally was the new 

 form introduced abroad among experimenters, few of whom 

 had ever seen the papers of Henry, that probably very few in- 

 deed have been aware to whom they were really indebted for 

 this familiar and powerful instrumentality. But the historic 

 fact remains, that prior to Henry's experiments in 1829, no 

 one on either hemisphere had ever thought of winding the 

 limbs of an electro-magnet on the principle of the 'bobbin,' 

 and not till after the publication of Henry's method in January 

 of 1 83 1, was it ever employed by any European physicist. 



"^ Philosophical Magazine, London, March, 1832, Volume xi, page 199. 



