SECT, xxxn.] ELECTEO-DYNAMICS. 361 



SECTION XXXII. 



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. 



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 con- 

 ducting 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 phe- 

 nomena 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, di- 

 verging, converging, circular, or heliacal, all produce 

 different kinds of motion in a conducting wire, both recti- 

 lineal and circular, and also the rotation of a wire helix, 

 such as that described, now called an electro-dynamic 

 cylinder on account of some improvements in its con- 

 struction (N. 219). And, as the hypothesis of a force 

 varying inversely as the squares of the distances 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 



