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possible : the scientific principles on 'wliicli it is founded were then 

 unknown. The first fact of electro-magnetism was discovered by Oersted, 

 of Copenhagen, durhig that winter. It is this : A wire being placed 

 close above, or below, and parallel to a magnetic needle, and a galvanic 

 current being transmitted through the wire, the needle will tend to place 

 itself at right angles to it. This fact was widely published, and the 

 account was everywhere received with interest. 



The second fact of importance was discovered independently, and about 

 the same time, by Arago, at Paris, and Davy, at London. It is this: 

 During the transmission of a galvanic current through a wire of copper, 

 or any other metal, the wire exhibits magnetic properties, attracting iron, 

 but not copper filings, and having the power of inducing permanent mag- 

 netism in steel needles. The next important fact was discovered by 

 Ampere, of Paris, one of the most sagacious and successful cultivators of 

 physical science in the present century. It is this : Two parallel wires 

 through which galvanic currents are passing in the same direction, attract 

 each other ; but if the currents pass in opposite directions, they repel 

 each other. On this fact Ampere founded his ingenious theory of mag- 

 netism and electro-magnetism. According to this theory, all magnetic 

 phenomena result from the attraction or repulsion of electric currents, 

 supposed to exist in the iron at right angles to the length of the bar ; and 

 that all the phenomena of magnetism and electro-magnetism are thus 

 referred to one principle, namely, the action of electrical currents on each 

 other. 



Ampere deduced from this theory many interesting results, which were 

 afterwards verified by experiment. He also proposed to the French 

 Academy a plan for the application of electro-magnetism to the transmis- 

 sion of intelligence to a distance ; this consisted in deflecting a number 

 of needles at the place of receiving intelligence, by galvanic currents 

 transmitted through long wires. This transmission was to be efiected by 

 completing a galvanic circuit. When completed, the needle was deflected. 

 "When interrupted, it returned to its ordinary position, under the influence 

 of the attraction of the earth. This project of Ampere was never reduced 

 to practice. All these discoveries and results were prior to 1823. 



The next investigations relating to the magnetic telegraph were pub- 

 lished in 1825 ; they were by Mr. Barlow, of the Royal Military Acad- 

 emy of Woolwich, England. He found that there was great diminution 

 in the power of a galvanic current to produce effects with an increase of 

 distance ; a diminution so great in a distance of two hundred feet was 

 observed, as to convince him of the impracticability of the scheme of the 

 electro-magnetic telegraph. His experiments led him to conclude that 

 the power was inversely as the square root of the length of the wire. The 



