ACTION AT A DISTANCE. 319 



matically as an interesting curiosity of science. But let us hear Faraday 

 himself, as he introduces to his reader the method which in his hands became 

 so powerful*. 



"It would be a voluntary and unnecessary abandonment of most valuable 

 aid if an experimentalist, who chooses to consider magnetic power as represented 

 by lines of magnetic force, were to deny himself the use of iron filings. By 

 their employment he may make many conditions of the power, even in com- 

 plicated cases, visible to the eye at once, may trace the varying direction of 

 the lines of force and determine the relative polarity, may observe in which 

 direction the power is increasing or diminishing, and in complex systems may 

 determine the neutral points, or places where there is neither polarity nor 

 power, even when they occur in the midst of powerful magnets. By their use 

 probable results may be seen at once, and many a valuable suggestion gained 

 for future leading experiments." 



Experiment on Lines of Force. 



In this experiment each filing becomes a little magnet. The poles of oppo- 

 site names belonging to different filings attract each other and stick together, 

 and more filings attach themselves to the exposed poles, that is, to the ends 

 of the row of filings. In this way the filings, instead of forming a confused 

 system of dots over the paper, draw together, filing to filing, till long fibres 

 of filings are formed, which indicate by their direction the lines of force in 

 every part of the field. 



The mathematicians saw in this experiment nothing but a method of exhibit- 

 ing at one view the direction in different places of the resultant of two forces, 

 one directed to each pole of the magnet ; a somewhat complicated result of 

 the simple law of force. 



But Faraday, by a series of steps as remarkable for their geometrical 

 definiteness as for their speculative ingenuity, imparted to his conception of these 

 lines of force a clearness and precision far in advance of that with which the 

 mathematicians could then invest their own formulae. 



In the first place, Faraday's lines of force are not to be considered merely 

 as individuals, but as forming a system, drawn in space in a definite manner 



* Exp. Res. 3284. 



