ELECTKO-MAGXETISM. 



429 



one force. Both are supposed to consist of two fluids, which repel their own 

 kind, and attract the opposite. The fluid in both cases is supposed to reside 

 upon the surface of bodies; the laws of induction in both are the same; and 

 each can be made to excite or develop the other. 



CHAPTER XIX. 



ELECTRC :^^agnetism:. 



What is Eiec- 803. Magnetism c.e'-eloped through the 

 tro-magaetismf ageiicy of elcctrical or chemical action, is 

 termed Electro-magnetism. 



Among the earliest phenomena observed which indicated a connection be- 

 tween magnetism and electricit3-, it was noticed that ships' compasses have 

 their directive power impaired by lightning, and that sewing needles are ren- 

 dered magnetic by electric discharges passed thi-ough them. 



In 1820, a discovery was made by Professor Oersted of 

 Denmark, which established beyond a doubt the connection 

 of electricity and magnetism. He ascertained that a mag- 

 netic needle brought near to a wire, through which an electric 

 current was circulating, was compelled to change its natural 

 direction, and that the new direction it assumed was determined by its position in 

 relation to the wire and to the direction of the current transmitted along the wire. 

 Further experiments developed the foUowing law: — 



Electric currents exert a magnetic influence 



at right angles with the direction of their flow, 



and when they act upon a magnetic needle 



Fig. 358. they tend to cause the needle 



^ to assume a position at right 



angles to the direction of the 



current. 



Thus, suppose an electric current to 

 pass on the wire A B, Fig. 358, in tiia 

 direction of the arrow ; suppose a mag- 

 netic needle, X S, to be placed directly 

 under the wire and parallel to it. By 

 the action of the electric current flowing 

 in the direction A B, the needle is caused 

 to move from its north and south posi- 

 tion and turn round, and if the current 



What effect is 

 produced when 

 a magnetic nee- 

 dle is brought 

 near a conduct- 

 ing wire? 



In what direc- 

 tion do electric 

 currents exert 

 their iutlaeuce? 



33 



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