SCIENCE OF COMMON THINGS. 299 



Electro-magnetism. When and how discovered. 



CHAPTER IY. 



ELECTRO-MAGNETISM. 

 1933 What is electro-magnetism f 



It is the magnetism developed through the agency 

 of electrical or galvanic action. 



1034 What were the earliest phenomena observed which indicated a 

 relation between magnetism and electricity f 



It was noticed that ship's compasses have their direc- 

 tive power impaired by lightning, and that sewing 

 needles could be rendered magnetic by electric dis- 

 charges passed through them. 



1935 What discovery, made by Prof. Oersted of Copenhagen, esta- 

 blished beyond a doubt the connection of electricity and magnetism f 



He ascertained that a magnetic needle placed near a 

 metallic wire connecting the poles of a galvanic battery 

 was compelled to change its direction, and that the new 



direction it assumed was deter- 

 mined by its position in rela- 

 tion to the wire and to the di- 

 rection of the current trans- 

 mitted along the wire. 



Thus, if, as in Fig. 94, a needle be in- 

 Fig. 94. closed in a wire not touching it at any 



point, and a current of electricity pass 



through the wire, the needle will be made to move in accordance with the 

 direction of the current 



1036 What other important discovery was made about the same 

 time ? 



It was found that if a piece of soft iron, not possessing 

 magnetic power sufficient to elevate a grain weight, be 

 placed within a coil of copper wire through which a 

 galvanic current is passing, it will become, through the 

 influence of the current, a powerful magnet ; and will, 

 so long as the current flows, sustain weights amount- 

 ing to many hundreds of pounds. (See figs. 95 and 

 96.) 



