314 ELECTRO-MAGNETISM. SECT. XXXI. 



SECTION XXXI. 



Discovery of Electro-Magnetism Deflection 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 

 Suspension of a Needle in a Helix Electro-Magnetic Induction Tem- 

 porary Magnets The Galvanometer. 



THE disturbing effects of the aurora borealis and light- 

 .ning 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 mag- 

 netized needle. This observation has given rise to the 

 theory of electro-magnetism the most interesting sci- 

 ence of modern times, whether it be considered as lead- 

 ing 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 fric- 

 tion, and the obstacle of a resisting medium, maintains 

 a perpetual motion, often vainly attempted, but appa- 

 rently 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 connect- 

 ed 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 north toward the east 

 or west, according to the direction in which the current 

 is flowing ; and on reversing the direction of the current, 

 the motion of the needle will be reversed also. The 

 numerous experiments that have been made on the 

 magnetic and electric fluids, as well as those on the vari- 

 ous relative motions of a magnetic needle under the 

 influence of galvanic electricity, arising from all possible 



