Royal Society. 69 



If the external part of the loop be retained fixed, as also the axial 

 part, and the magnet with the short radial part of the wire be 

 revolved, an electric current is again produced, of a strength exactly 

 equal to the former for the same number of degrees of revolution ; 

 but its direction is the reverse of the first current, when the direction 

 of revolution is the same. In either case, reversing the direction of 

 the revolution reverses the current produced by it. The moving 

 radial part of the wire is in this case insulated from the magnet, 

 and many other experiments, as with discs at the ends of the magnet, 

 show, that the motion of the magnet itself is indifferent j and that 

 whether it revolve or is still, provided the wire move, the result is 

 the same. When the radial wire or part of the loop, and the ex- 

 ternal part move together, then their effects exactly neutralize each 

 other, as they ought to do, being in contrary directions, for the 

 same revolution ; and not the slightest trace of a current under the 

 extremest conditions of motion, or of the experiment, can be per- 

 ceived. Such is the case, whatever the course or distance of the 

 external part of the loop may be, or even when the loop is altogether 

 external to the magnet, but moving at the same angular velocity 

 either with or around it. 



When the axial part of the loop is revolved it produces no effect; 

 neither if this part revolve or be still does it produce the least 

 influence on any of the results already described ; it acts simply as 

 a conductor, and is in other respects perfectly indifferent. This 

 axial wire may be replaced by the magnet itself; for when it exists 

 only from the magnetic pole outwards, and when the radial wire 

 has contact with the magnets at the centre, so as to complete the 

 electric circuit, the results are exactly the same as before : or the 

 axial wire may proceed to the centre and then make contact with 

 the magnet, and the radial wire be removed ; when precisely the 

 same results occur : or both axial and radial parts may be removed, 

 the magnet serving both for conductor and moving radius, and still 

 the results are unchanged. 



From such results as these, the author draws the following con- 

 clusions, in relation to the lines of magnetic force as defined at the 

 commencement. The amount of magnetic force (as shown by the 

 electric current evolved) is determinate ; and the same for the same 

 lines of force, whatever the distance of the point or plane on which 

 their power is exerted is from the magnet : or it is the same in any 

 two or more sections of the same lines of force. There is no loss 

 or destructibility, or evanescence or latent state of the magnetic 

 power. Convergence or divergence of the lines of force causes no 

 difference in the amount of their power. Obliquity of intersection 

 causes no difference. In an equal field of magnetic force the elec- 

 tricity evolved is proportionate to the time of motion, or to the 

 velocity of motion, or to the amount of lines of force intersected. 



The internal state of the magnet is then examined by means of 

 the results obtained with the radial wire, or the moving magnet 

 when the latter makes part of the circuit; and the conclusion is 

 arrived at, that there arc within the magnet lines of magnetic fore 



