248 BULLETIN OP THE 



tation of the electro-magnet, the compass needle v/as repelled 

 from one leg (by its similar magnetism) and attracted by the 

 other leg, so that its free end tapped the bell. This simple 

 device the Professor was accustomed to exhibit to his classes, in 

 illustration of the facility of transmitting signals to a distance by 

 the swift action of electro-magnetism. 



Henry regarded his "quantity" magnet as h^mg scientifically 

 more important than his "intensity" magnet; and his success in 

 constructing such, of almost incredible power, caused numerous 

 requisitions on his skill. In April, 1831, Professor Silliman pub- 

 lished in his Journal "An Account of a large Electro-Magnet 

 made for the Laboratory of Yale College," under his charge. 

 The iron horse-shoe about one foot high was made from a three 

 inch octagonal bar 30 inches long ; and was wrapped with 26 

 strands of copper wire each about 28 feet long. When duly 

 excited by a single galvanic element consisting of concentric 

 cylinders of copper and zinc, presenting about five square feet of 

 active surface, the magnet lifted more than a ton weight. For 

 reversing the polarity of the magnet, a duplicate battery was 

 oppositely connected with extensions of the ends of the coils, so 

 that either battery could be alternately dipped. With a load of 

 56 pounds suspended from the armature, the poles of the magnet 

 could be so rapidly reversed, that the weight would not fall. 

 Professor Silliman remarks of the maker: " He has the honor of 

 having constructed by far the most powerful magnets that have 

 been known ; and his last, weighing (armature and all) but S2|- 

 pounds, sustains over a ton ; — which is eight times more powerful 

 than any magnet hitherto known in Europe."* And Sturgeon 

 (the true foster-father of the magnet) thus heralds the Yale Col- 

 lege triumph : " By dividing about 800 feet of conducting wire 

 into 26 strands and forming it into as many separate coils around 

 a bar of soft iron about 60 pounds in weight and properly bent 

 into a 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 oriental im- 

 poster in his iron coffin, "f 



J7?(? first Electro-magnetic Engine. — Among his ingenious 

 applications of the new power, Henry's invention of the Elec- 

 tro-magnetic Engine should here be noticed. In a letter to 



* Sillirhan's Am. Jour. Sci. April, 1831, vol. xx. p. 201. Relatively, 

 some of Henry's smaller magnets were many times more powerful than 

 this. A miniature one made by Dr. Ten-Eyck under his direction, sus- 

 tained 200 times its own weight ; and one still smaller, sustained more 

 than 400 times its own weight! (Sill. Am. Jour. Sci. vol. xix. p. 407.) 



t Philosoph. Magazine; and Annah, 1832, vol. xi. p. 199. 



22 



