Prof. Faraday on some Points of Magnetic Philosophy. 101 



reciprocally, is easily taken cognizance of by spirals, &c. as 

 regards any change in direction or degree. Then consider the 

 medium a, a, a to be all copper or all mercury, still the forces 

 are undisturbed : or consider it part mercury or copper, and 

 part vacuum or glass, divided either by a line running from S 

 to N, or along a a a, or any other way, still the forces are un- 

 disturbed ; any of these media act exactly like space, or so like 

 it, we can scarcely trace a difference. Then consider the metal 

 moving, either as a finely divided stream at a, a, a, or as a 

 solid globe (of copper) C, fig. 7, revolving rapidly round the line 

 from N to S ; still it is exactly like the vacuum or jv^ « 

 indifferent gas or glass, and there is no effect as yet 

 by which we might distinguish the material medium 

 from the mere space. But let the stream of me- 

 tallic particles be converted into a continuous plate, 

 and then we know it becomes filled with abundant 

 currents of electricity ; or if we apply the wires of 

 a galvanometer to the revolving copper globe C, 

 at the axial and equatorial parts, we can then cause it to 

 develope (by permission of currents) a new effect, and the cur- 

 rents are sent out most abundantly by the conductors applied. 

 If the copper globe C be rapidly revolved upon an axis per- 

 pendicular to the line S N, so strong and influential a me- 

 dium is it, magnetically considered, that the two poles, N and S, 

 if free to move, do move in the same direction as the near parts 

 of the globe ; and are absolutely carried away from each other, 

 in opposition to their mutually attractive force, which tends 

 strongly all the while to draw them together. Now, how is it 

 possible to conceive that the copper or mercury could have this 

 power in the moving state, if it had no relation at all to the 

 magnetic force in the fixed state ? or, that it should have like 

 power in the compact state, and yet have no relation to the 

 magnetic force in the divided and moving state ? The mere 

 addition of motion could do nothing, unless there were a prior 

 static dependence of the magnet and the metal upon each other. 

 We know very well that the actions in the moving cases involve 

 the evolution, or a tendency to the evolution, of electric cur- 

 rents ; but that knowledge is further proof that the metals are 

 in prior relation to the magnetic forces ; and as bodies, even 

 down to aqueous solution, have these electric currents set up in 

 them under like circumstances, we have full reason to believe 

 that all bodies when in the magnetic field are in like static re- 

 lation as the copper when not moving : — and that when motion 

 is superadded, they would all evolve electric currents, were it 

 not for their bad electro-conducting powers. 



3338. These effects of motion are known to be identical with 



