124 LEADING AMERICAN MEN OF SCIENCE 



well have seemed to his fellows as a man who, though possessing 

 great talents was ready to waste his time in investigating matters 

 of no human interest. But instead of taking this view he received 

 such encouragement and support that he was enabled to continue 

 investigations into the laws of electricity, and to make new dis- 

 coveries which have since proved to be of great practical impor- 

 tance in the application of that agent. To give a clear idea of a 

 few of these investigations we must recall some of the laws of 

 electricity. 



Before Henry's time it was known that, when a wire was 

 wrapped around a piece of iron, and an electric current passed 

 through the wire, the iron instantly became a magnet, attract- 

 ing every piece of iron in its neighborhood. If the iron was 

 well annealed and soft, it lost its magnetism, and its attraction 

 ceased the moment the current was interrupted. Every one 

 who has seen the Morse telegraph at work knows it is by this 

 property of the electric current that messages are transmitted. 

 Henry's first experiments were devoted to showing how the 

 power of a single battery to produce this effect could be enor- 

 mously increased by passing more and more coils around the 

 magnet. Carrying forward his experiments he made enormous 

 magnets which held up weights greater than anyone had before 

 supposed a magnet could ever do. With a battery having a 

 single plate of zinc, of half a square foot of surface, he made a 

 magnet lift a weight of 750 pounds, more than thirty-five 

 times its own weight. In connection with this experiment he 

 showed the difference between the quantity of electricity and 

 its projectile force, a distinction at the base of all modern appli- 

 ances of electricity. 



At Albany in 1831-32 Henry showed for the first time how 

 easily an electric telegraph could be constructed. He ran the 

 wires of an electric circuit several miles in length around one of 

 the upper rooms in the Albany Academy. An electric current 

 was sent around this circuit from a small battery passing in its 

 course through the coils of an electromagnet. A permanent 

 magnet was swung between the poles of this electromagnet in 



