DISCOURSE OF W. B. TAYLOR. 229 



contact with a leg of the soft iron core, while near the opposite end 

 of the compass rod, a small stationary office-bell was placed. At 

 each excitation of the electro-magnet, the compass rod or needle was 

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

 the other leg, so that its free end tapped the bell. On a reversal of 

 the current, the compass rod moved back to the opposite leg of the 

 electro-magnet. This simple device the Professor was accustomed 

 to exhibit to his classes, during the years 1831 and 1832, in illus- 

 tration of the facility of transmitting signals to a distance by the 

 swift action of electro-magnetism.* 



Henry regarded his "quantity" magnet as being scientijically 

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

 constructing snc^h, 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 

 horseshoe 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 

 galvanie element consisting of concentric cylinders of copper and 

 zinc, presenting about five square feet of active surface, the magnet 

 lifted 2,300 pounds, 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 during the interval of inversion. 

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

 having constructed by far the most powerful magnets that have ever 

 been known ; and his last, weighing (armature and all) but 82| 

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

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



* For an account of Henry's relation to the electro-magnetic Telegraph, see " Sup- 

 plement," Note C. 



tSllliman'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, sustained 200 times its own weight ; and one 

 still smaller, sustained more than 400 times its own weight! (Sill. Am. Jour. Sci. 

 Tol. xlx. p. 407.) 



