Mechanical Science. 609 



14. POWERFUL ELECTRO-MAGNETS. 



Professor Henry, of the Albany Academy, and Dr. Ten Eyck, have 

 extended the ingenious experiments of Mr. Sturgeon, by adopting 

 the principle of Professor Schweiger's galvanometer, and produced 

 magnetic effects on soft iron, which we could scarcely have expected 

 from the feeble voltaic current which they employed. The circum- 

 stances on which the increase of electro-magnetic power depends, 

 are, first an increase of the mass of soft iron ; and secondly an 

 increase in the number of coils without increasing the length of the 

 wire. 



A cylindrical bar of soft iron, ten inches long and half an inch 

 diameter, was bent into the form of a horseshoe, and wound with 

 thirty feet of copper wire, covered with silk thread. With a pair of 

 plates two inches and a half square, dipped into dilute acid, the soft 

 iron became a magnet capable of raising fourteen pounds. A wire 

 of the same length as the first was wound over it, and the ends sol- 

 dered to the copper and zinc plates : the effect was now doubled, and 

 the temporary magnet actually supported twenty-eight pounds. 

 With plates of four inches by six, it supported more than fifty times 

 its own weight. 



But the greatest effect which has ever been produced on soft iron 

 by voltaic electricity was, by using a bar of iron two inches square and 

 twenty inches long, having the edges rounded and being bent into the 

 form of a horseshoe magnet. Around the horseshoe 540 feet of copper 

 bell-wire was wound in nine coils of sixty feet each. These coils 

 were not continued from one end of the magnet to the other ; but 

 each of them was wound round a space of the horseshoe about one 

 inch long, leaving the ends of the lines projecting and properly 

 numbered. By soldering the alternate ends to a copper cylinder, 

 and the others to a smaller cylinder of zinc, containing only two- 

 fifths of a square foot, and placing the one within the other in dilute 

 acid, the following extraordinary effect was produced. When the 

 armature of soft iron was placed across the ends of the horseshoe, 

 and weights added till the temporary magnet could support no more, 

 it was found that the total weight amounted to 650 pounds, an as- 

 tonishing effect for such a small battery, and requiring only half a 

 pint of dilute acid for its submersion. With a larger battery the 

 weight raised was 750 pounds, which seemed to be the maximum of 

 magnetic power which could be developed in that bar by voltaic 

 electricity. This appears to be the strongest magnet ever con- 

 structed, either by the ordinary modes of magnetizing steel bars, or 

 by the voltaic current. Mr. Peal's magnet weighs fifty-three 

 pounds, and lifts 310 pounds, or about six times its own weight; 

 whereas this temporary one weighs only twenty-one pounds, and 

 raises more than thirty- five times its own weight. 



When the ends of the wires were united so as to form a continuous 

 wire of 540 feet, the weight raised was only 145 pounds. 



When a battery containing twenty-five double plates, and pre- 

 senting the same surface with the cylindrical battery, was employed, 



