Masterpieces of Science 



laws of interaction between currents and mag- 

 nets he hoped to deduce the motion observed by 

 Arago. That hope he realized, showing by 

 actual experiment that when his disk rotated 

 currents passed through it, their position and 

 direction being such as must, in accordance with 

 the established laws of electro-magnetic action, 

 produce the observed rotation. 



Introducing the edge of his disk between the 

 poles of the large horseshoe magnet of the Royal 

 Society, and connecting the axis and the edge 

 of the disk, each by a wire with a galvanometer, 

 he obtained, when the disk was turned round, 

 a constant flow of electricity. The direction of 

 the current was determined by the direction of 

 the motion, the current being reversed when the 

 rotation was reversed. He now states the law 

 which rules the production of currents in both 

 disks and wires, and in so doing uses, for the 

 first time, a phrase which has since become 

 famous. When iron filings are scattered over a 

 magnet, the particles of iron arrange themselves 

 in certain determined lines called magnetic curves. 

 In 1831, Faraday for the first time called these 

 curves "lines of magnetic force; " and he showed 

 that to produce induced currents neither approach 

 to nor withdrawal from a magnetic source, or 

 centre, or pole, was essential, but that it was 

 only necessary to cut appropriately the lines of 

 magnetic force. Faraday's first paper on 

 Magneto-electric Induction, which I have 

 here endeavoured to condense, was read 

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