Scr. XXXII. ELECTRO-DYNAMICS. 319 



SECTION XXXII. 



Electro- Dynamics Reciprocal Action of Electric Currents Identity of 

 Electro-Dynamic Cylinders and Magnets Differences between the Ac- 

 tion of Voltaic Electricity and Electricity of Tension Effects of a Voltaic 

 Current Ampere's Theory. 



THE science of electro-magnetism, which must ren- 

 der 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 elec- 

 trical currents on one another, has added a new branch 

 to the subject, to which he has given the name of elec- 

 tro-dynamics. 



When electric currents are passing through two con- 

 ducting wires, so suspended or supported as to be capa- 

 ble of moving both toward ?.nd from one another, they 

 show mutual attraction or repulsion, according as the 

 currents are flowing in the same or in contrary direc- 

 tions ; the phenomena varying with the relative inclina- 

 tions 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 circular, and also the rotation 

 of a wire helix, such as that described, now called aii 

 electro-dynamic cylinder, on account of some improve- 

 ments in its construction (N. 219). And as the hypoth- 

 esis of a force varying inversely as the squares of the 

 distances accords perfectly with all the observed phe- 

 nomena, 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 hi a direction 

 similar to the motion of the hands of a watch, acts as the 

 south pole of a magnet, and the other end, in which the 



