316 ELECTRO-DYNAMICS. SECT. XXXI. 



SECTION XXXI. 



Electro-Dynamics Reciprocal Action of Electric Currents Identity of 

 Electro-Dynamic Cylinders and Magnets Differences between the Action 

 of Voltaic Electricity and Electricity of Tension Effects of a Voltaic 

 Current Ampere's Theory Dr. Faraday's Experiment of Electrifying 

 and Magnetising a Ray of Light. 



THE science of electro-magnetism, which must render the name 

 of M. Oersted ever memorable, relates to the reciprocal action of 

 electrical and magnetic currents : M. Ampere, by discovering the 

 mutual action of electrical currents on one another, has added a 

 new branch to the subject, to which he has given the name of 

 electro-dynamics. 



When electric currents are passing through two conducting 

 wires, so suspended or supported as to be capable of moving both 

 towards and from one another, they show mutual attraction or 

 repulsion, according as the currents are flowing in the same or in 

 contrary directions ; the phenomena varying with the relative 

 inclinations and positions of the streams of electricity. The 

 mutual action of such currents, whether they flow in the same or 

 in contrary directions, whether they be parallel, perpendicular, 

 diverging, converging, circular, or heliacal, all produce different 

 kinds of motion in a conducting wire, both rectilineal and circu- 

 lar, and also the rotation of a wire helix, such as that described, 

 now called an electro-dynamic cylinder on account of some im- 

 provements in its construction (N. 225). And, as the hypothesis 

 of a force varying inversely as the square of the distance accords 

 perfectly with all the observed phenomena, these motions come 

 under the same laws of dynamics and analysis as any other 

 branch of physics. 



Electro-dynamic cylinders act on each other precisely as if 

 they were magnets during the time the electricity is flowing 

 through them. All the experiments that can be performed with 

 the cylinder might be accomplished with a magnet. That end of 

 the cylinder in which the current of positive electricity is moving 

 in a direction similar to the motion of the hands of a watch, acts 



