SCIENCE IN THE INDUSTRIAL WORLD 



The study of these electromagnets was taken up by 

 Prof. Joseph Henry in America, who succeeded in 

 producing some remarkable magnets of this type. 

 One of these which he made in 1833 is still in the pos- 

 session of Yale University. It weighs about one hundred 

 pounds, and was capable of sustaining a weight of 

 thirty-five hundred pounds. Professor Henry was in 

 the habit of giving in his class-room and at lectures 

 some extremely interesting demonstrations of the power 

 of his magnets. One of these was to suspend an electro- 

 magnet, connected with an apparatus whereby the cur- 

 rent of electricity in the surrounding coils could be 

 rapidly turned on and off, from a frame. A heavy 

 weight of iron, ranging from twenty-five pounds upward, 

 was then attached and held in place on the under 

 surface of the magnet. By setting in motion the ap- 

 paratus for rapidly making and breaking the current, 

 this heavy iron weight was made to perform a series of 

 rebounds against the magnet with a force and sound of a 

 trip-hammer, or of rapid hammering on an anvil. 



The simple explanation of this astonishing exhibition 

 was that two forces, gravitation and magnetism, acted 

 alternately upon the iron weight. Gravity caused it to 

 fall when the current was broken, but before it could 

 fall far enough to be beyond the controlling power of 

 the magnet, the circuit would be again closed, causing 

 the weight to fly back against the core of the magnet. 



THE FIRST PRACTICAL TELEGRAPH SYSTEM 



This discovery of the electromagnet was at once 

 seized upon by inventors interested in the telegraph 



[16] 



