8o 



NATURE 



\_Nov. iZ, 1878 



attractions and repulsions iiad been explained as a kind 

 of action-at-a-distance. Faraday explained them as 

 the results of the action of the medium filling the inter- 

 vening space ; and he gave several indisputable proofs 

 that the space surrounding a magnet was thrown into a 

 peculiar condition by the presence of the magnetism. 

 Two centuries previously another Englishman, as uniquely 



Fig. I. 



great if not greater, Dr. Gilbert, had in his famous 

 treatise " De Magnete," told how iron filings sprinkled on 

 a piece of card beneath which a magnet lay, assumed 

 certain mysterious lines. To these lines Faraday gave 

 the name of lines of force, and showed that they repre- 

 sented, wherever they went, the direction and strength of 



the magnetic forcei His imagination seized upon these 

 mysterious lines, and he saw all space, wherever a mag- 

 net had influence, traversed by them. He perceived 

 that they were in seme way bound up with that which 

 was mysterious and unexplained in this seeing action-at- 

 a-distance. He found them to react on one another, 

 and to follow certain definite laws ascertainable by 



experiment. In the volumes of his researches he filled 

 several entire plates with drawings of the figures assumed 

 by the lines under various combinations. They had 

 taught him to anticipate magneto-electricity and electro- 

 magnetic rotation. He' had diligently followed them up 

 froni the hint afforded by Dr. Gilbert's experiment with 

 the iron filings. He had begun to apply the method to 



Fig. s. 



the investigation of the interaction of electric currents, 

 when the decay of age overtook him, and the research 

 dropped from his grasp. Had he lived the study which 

 the writer of the present article is about to narrate 

 would have been completed long ago. 



The experiment of laying a card or a sheet of paper 



Fig. 4. 



upon a magnet, sprinkling over it fine iron filings, and 

 then tapping the card gently so as to allow the filings to 

 take up their places in the "curving lines of force," is 

 one which always possesses a peculiar interest and 

 fascination for youthful electricians. Two other experi- 

 ments, due originally to Musschenbroek, are not quite so 

 familiar, though they are as simple ; and since they have 



