Faraday as a Discoverer. 47 
plication, and in refusing to assent to the imperfect theories of 
others.” Now, however, the time for theory had come. Fara- 
day saw mentally the rotating disk under the operation of the 
magnet flooded with his induced currents ; and from the known 
laws of interaction between currents and magnets he hoped to 
deduce the motion observed by Arago. That hope he realized, 
showing by actual experiment that when his disk rotated cur- 
rents 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 gal- 
vanometer, 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 whic 
has since become famous. When iron filings are scattered 
over a magnet, the particles of iron arrange themselves in 
certain determinate 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 froma magnetic source, or center, 
or pole, was essential, but that it was only necessary to cut 
appropriately the lines of magnetic force. _Faraday’s first pa- 
on magneto-electric induction, which I have here endeay- 
ored to condense, was read before the Royal Society on the 
24th of November, 1831. 
On the 12th of January, 1832, he communicated to the 
Royal Society a second paper on Terrestrial Magneto-electric 
