194 CLASSICS OF MODERN SCIENCE 

 could be all the effects which induction by currents could produce; 

 especially as, upon dispensing with iron, almost the whole of them 

 disappear, whilst yet an infinity of bodies, exhibiting definite phe- 

 nomena of induction with electricity of tension still remain to be acted 

 upon by the induction of electricity in motion. 



3. Further : whether Ampere's beautiful theory were adopted, or 

 any other, or whatever reservation were mentally made, still it ap- 

 peared very extraordinary, that, as every electric current was accom- 

 panied by a corresponding intensity of magnetic action at right angles 

 to the current, good conductors of electricity, when placed within the 

 sphere of this action, should not have any current induced through 

 them, or some sensible effect produced equivalent in force to such a 

 current. 



4. These considerations, with their consequence, the hope of ob- 

 taining electricity from ordinary magnetism, have stimulated me at 

 various times to investigate experim,entally the inductive effect of 

 electric currents. I lately arrived at positive results ; and not only 

 had my hopes fulfilled, but obtained a key which appeared to me to 

 open out a full explanation of Arago's magnetic phenomena, and also 

 to discover a new state, which may probably have great influence in 

 some of the most important effects of electric currents. 



5. These results I purpose describing, not as they were obtained, 

 but in such a manner as to give the most concise view of the whole. 



EVOLUTION OF ELECTRICITY FROM MAGNETISM 



2y. A welded ring was made of soft round bar-iron, the metal 

 being seven-eighths of an inch in thickness, and the ring six inches in 

 external diameter. Three helices were put round one part of this 

 ring, each containing about twenty-four feet of copper wire one- 

 twentieth of an inch thick ; they were insulated from the iron and 

 each other, and superposed in the manner before described (6), oc- 

 cupying about nine inches in length upon the ring. They could be 

 used separately or conjointly ; the group may be distinguished by the 

 letter A. On the other part of the ring about sixty feet of similar 

 copper wire in two pieces were applied in the same manner, forming 

 a helix B, which had the same common direction with the helices of 

 A, but being separated from it at each extremity by about half an 

 inch of the uncovered iron. 



