ELECTRO-MAGNETISM. 



433 



Has electro- 

 magnetic force 

 been applied 

 to any prac- 

 tical purpose 

 for propelling 

 machinery? 



Fig. 366. ^ *^o semicircular rings of soft iron be passed within a 



helical ring, as is represented in Fig. 3G6, thej will become so 

 strongly magnetic on passing the current of even a small 

 battery, as to be separated with extreme difficulty. A rod 

 of iron brought near to one of the extremities of a longitudinal 

 helix, is not only attracted but lifted up into the center of the 

 coil, where it remains suspended without contact or visibls 

 support, so long as the current continues in action. If tha 

 battery and helix be of sufficient size, a considerable weight 

 may be suspended. In some experiments at the Smithsonian 

 Institution at "Washington, a few years since, a bar of iron 

 weighing 80 pounds was raised and suspended in the air with- 

 out being in contact with any body. 



806. Many attempts have been made to 

 take advantage of the enormous force gener- 

 ated and destroyed, in an instant, by making 

 or breaking an electric current, for propelling 

 machinery, but thus far all efforts have failed 



to produce any practical results. 



One of the reasons why this power can not be used to advantage is, that 

 tb.e rate at which the power diminishes as we recede from the contact point 

 of tho magnets, prevents our obtaining the full force of the magnets. Thus, 

 a magnet whose force in contact would be sufficient to raise 250 pounds, 

 would exert a force of only 90 pounds at the distance of l-250th of an inch, 

 and of only 40 pounds at the distance of 1 -50th of an inch. It is also found 

 that notwithstanding the lo^ of power with distance, a still greater loss takes 

 place with motion. The moment any magnetic body is moved in front of 

 either a permanent or an electro-magnet it loses power, and this loss increases 

 very rapidly with the increase of velocity. This obstacle stopped the prog- 

 ress of the very extensive researches of Professor Jacobi, after he had ex- 

 pended upward of $120,000 granted him for his experiments by the liber- 

 ahty of the Russian government 



807. The construction of the Morse mag-, 

 netic telegraph depends upon the principle, 

 that a current of electricity circulating about 

 a bar of soft iron temporarily renders it a 



magnet. 



The construction and method of operating the Jlorse telegraph may be 

 clearly understood by reference to Fig. 3G7. F and E are pieces of soft iron 

 surrounded by coils of wire, which are connected at a and b with wires pro- 

 ceeding from a galvanic battery. "When a current is transmitted from a bat- 

 tery located one, two, or three hundred miles distant, as the paae may be, it 



].q 



Upon -what 

 does the con- 

 Btruction of the 

 Morse tele- 

 graph depend ? 



