286 HENRY A. ROWLAND 



through vacant space: Newton felt this impossibility in the case of 

 gravitation, but it is to Faraday that we must look principally for the 

 idea that electrical and magnetic actions must be carried on by means 

 of a medium filling all space and usually called the ether. The develop- 

 ment of this idea leads to the modern theory of electrical phenomena. 



Take an ordinary steel magnet and, like Faraday, cover it with a 

 sheet of paper, and upon this sprinkle iron filings. Mapped before us 

 we see Faraday's lines of magnetic force extending from pole to pole. 

 We can calculate the form of these lines on the supposition that a 

 magnetic fluid is either distributed over the poles of the magnet or 

 on its molecules, assuming that attraction takes place through space 

 without an intervening medium. But at this idea the mind of Faraday 

 revolted, and he conceived that these lines, drawn for us by the iron 

 filings, actually exist in the ether surrounding the magnet; he even 

 conceived of them as having a tension along their length and a repul- 

 sion for one another perpendicular to their length. 



Two magnets, then, near each other, become connected by these lines, 

 which, like little elastic bands always pulling along their length, strive 

 to bring the magnets together. These so-called lines of force (now 

 called tubes of force) were, by his theory, conducted better by iron and 

 worse by bismuth than by the ether of space, and so gave the explana- 

 tion of magnetic attraction and diamagnetic repulsion. 



The same theory of lines of force was also applied by Faraday to 

 electrified bodies, and thus all electrostatic attractions were explained. 

 By this idea of lines of force it will be seen that Faraday did away 

 with all action at a distance and with all magnetic and electrical fluids, 

 and substituted, instead, a system in which the ether surrounding the 

 magnet or the electrified body became the all-important factor and the 

 magnet or electrified body became simply the place where the lines of 

 force ended: where a line of magnetic force ended, there was a portion 

 of imaginary magnetic fluid: where a line of electric force ended, there 

 was a portion of imaginary electric fluid. As the quantities of so- 

 called plus and minus electricity in any system are equal, we can 

 thus imagine every charged electrical system to be composed of a 

 group of tubes of electrical force (more strictly electric induction) 

 which unite the plus and minus electrified bodies, each unit tube having 

 one unit of plus electricity on one end and one unit of minus electricity 

 on the other. The tension along the tube explains the reason why 

 such an arrangement acts as if there were real plus and minus elec- 

 trical fluids on the ends of the tube, attracting one another at a dis- 



