326 Mr. W. Sturgeon o)i the Distribution ajid Retetiiiofi 



was in one position, and sometimes when in another. The 

 needle was evidently affected in whatever position the magnet 

 was placed; but I soon found that it would oscillate with the 

 plate whether the magnet was present or not. I might per- 

 haps have expected that this would be the case, by taking into 

 consideration that the needle itself would magnetize the disc. 

 I observed, however, that the needle was not only more pow- 

 erfully affected during the presence of the magnet, but that it 

 would, in some positions, move in an opposite direction to that 

 of the disc. Moreover, the deflections evidently varied by 

 placing the needle on opposite sides, indicating something 

 Uke a north polarity on one side of the disc, and a south po- 

 larity on the other side. Neither were these apjiearances 

 uniform in all parts of the same side ; for in some places 

 there appeared a north polar action, and in others as decided 

 a south polar action. It would be unnecessary, however, to 

 describe the various observations which I made by these first 

 experiments ; it will be sufficient to remark, that it was soon 

 discovered that this mode of experimenting was by no means 

 the best adapted for such an inquiry; for although this ar- 

 rangement of the apparatus showed most decidedly that the 

 magnetic force in the copper was distributed in a very pecu- 

 liar manner, yet, for want of command over the vibratory 

 motions of the disc and the needle, it was impossible to trace 

 it with precision in the area of the metallic surface. 



I next placed a disc of copper horizontally, so that it could 

 be oscillated or rotated in its own plane on a vertical axis; 

 and by erecting a thin stage over it, a common compass needle 

 could be placed over any part of its surface ; and as the axis 

 was connected with a multiplying wheel and band, a motion 

 of any required velocity could be given to the disc. By this 

 apparatus most of my experiments were made; and I very 

 soon found that no very great delicacy in the suspension of 

 the needle was necessary, and that one mounted on a pivot 

 was much better adapted for the investigation than one sus- 

 pended by a silken film. The investigation, however, was ex- 

 ceedingly tedious, and required the most rigid observation to 

 reconcile the phaenomena to any determinate law, or to trace 

 the various curves on the surface of the discs, over which the 

 needle would deviate in any required direction with reference 

 to these lines, by a constant standard direction in the motion 

 of the disc. And what still further increased the difficulty, it 

 was found that the distribution of the magnetic polarity varies 

 with almost every difference in the dimensions of the plate. 

 It also varies by the velocity, and again by the distance of the 

 magnetic poles from the centi'e of motion ; so that u))on the 



whole, 



