254 GREAT MEN OF SCIENCE 



depended upon a quite slight motion of the galvanometer 

 needle, was thenceforward the starting point from which 

 Faraday strove persistently to penetrate further into the 

 unknown. 



In the midst of work of the highest intensity, he then 

 brought to light, in the course of three months, a large num- 

 ber of the most important new facts. First, induction by 

 bringing together and separating the two conducting cir- 

 cuits, when no iron was present. Then we have mag- 

 netic induction, whereby Faraday first made use of a closed 

 ring of soft iron, which carried two windings of wire on oppo- 

 side sides; when the current was started and stopped in one 

 of these windings, the needle of a galvanometer connected to 

 the other was so strongly affected that it actually spun round 

 several times. This was the first observation of a powerful 

 inductive effect.^ 



He then used also iron rods with coils, and then he 

 proved that simple steel magnets can also produce induction 

 just as well as current-carrying coils, which fact entirely 

 agrees with Ampere's conception of magnetism. The know- 

 ledge thus obtained enabled Faraday also to give a direct 

 explanation of a group of phenomena discovered by Arago 

 seven years previously, hitherto unexplained, and known by 

 the name of rotation-magnetism. He then for the first time 

 drew off steady currents by means of rubbing contacts from 

 a copper disc, in which the current was generated by in- 

 duction, by rotating the disc between the poles of a magnet. 

 Finally he gave in the same first publication concerning in- 

 duction, the general law of these phenomena, which summed 

 up all the cases observed by him. It is a matter of the 

 cutting of magnetic lines of force by conductors, and this 

 entirely new kind of fundamental idea has also proved satis- 

 factory in regard to all further observed forms of induction. 



* A fine marble statue of Faraday lecturing with the ring in his hand, 

 is on the staircase of the Royal Institution. 



