SECT, xxxi.] ELECTRO-MAGNETISM. 355 



SECTION XXXI. 



Discovery of Electro-MagnetismDeflection of the Magnetic Needle by a 

 Current of Electricity Direction of the Force Rotatory Motion by Elec- 

 tricity Rotation of a Wire and a Magnet Rotation of a Magnet about its 

 Axis Of Mercury and Water Electro-Magnetic Cylinder or Helix Sus- 

 pension of a Needle in a Helix Electro-Magnetic Induction Temporary 

 Magnets The Galvano-Meter. 



THE disturbing effects of the aurora borealis and lightning 

 on the mariner's compass had been long known. In the 

 year 1819, M. Oersted, Professor of Natural Philosophy at 

 Copenhagen, discovered that a current of Voltaic electricity 

 exerts a powerful influence on a magnetized needle. This 

 observation has given rise to the theory of electro-mag- 

 netism the most interesting science of modern times, 

 whether it be considered as leading us a step farther in 

 generalization, by identifying two agencies hitherto referred 

 to different causes, or as developing a new force, unparalleled 

 in the system of the world, which, overcoming the retardation 

 from friction, and the obstacle of a resisting medium, main- 

 tains a perpetual motion, often vainly attempted, but ap- 

 parently impossible to be accomplished by means of any 

 other force or combination of forces than the one in question. 

 When the two poles of a Voltaic battery are connected by 

 a metallic wire, so as to complete a circuit, the electricity 

 flows without ceasing. If a straight portion of that wire 

 be placed parallel to, and horizontally above, a magnetized 

 needle at rest in the magnetic meridian, but freely poised 

 like the mariner's compass, the action of the electric current 

 flowing through the wire will instantly cause the needle to 

 change its position. Its extremity will deviate from the 



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