108 Prof. Faraday on some Points of Magnetic Philosophy. 



in the present case they show that weakened place, which in a 

 higher degree would be a place of no magnetic force. 



The moving conductor. 



3351. I wish to make a few further remarks (3336. 3337.) 

 upon the value of the moving conductor, as a means of investi- 

 gation in magnetical science. It will be sufficient to refer to 

 former papers for a statement of the principles, the power, 

 and the certainty of its indications (3156. 3172. 3176. 3270.). 

 At present, I desire to apply it in a direct form of experi- 

 ment, to the supposed reverse polarity of iron and bismuth 

 (3309.). 



3352. Four metallic spheres of copper, bismuth, soft iron, and 

 hard steel, - 8 of an inch in diameter, have been prepared ; each 

 has a copper axis carrying a small wooden pulley, so that when 

 in its supporting frame, rotation, more or less rapid, can be given 

 to it by the band of a multiplying wheel ; each also has a thin 

 copper ring driven tightly on to it at the equator, which, being 

 grooved, serves to retain a galvanometer wire pressed against 

 that part during the revolution of the globe ; the other wire 

 meanwhile being held against the copper axis. These globes, in 

 their frame, could be placed one by one in the magnetic field of 

 a powerful permanent Logeman 



magnet, so as to be subject to S- lcJ * 



the magnetic force, fig. 13 ; and 

 then rotated, and the currents 

 of electricity induced in them 

 carried to galvanometers. Two 

 suchinstrumentswereemployed, f '') 



one, a Ruhmkorff's, with fine ' s --' 



wire (2651.), the other with a thick wire of only four revolutions 

 (3178.). The latter was the best, but both gave good indications. 

 The position of all things concerned was preserved undisturbed 

 during the experiments, so that it will not be necessary to do 

 more than to describe a standard effect, and afterwards refer 

 other effects to it. This standard may be taken from the current 

 indicated when the copper globe was in the magnetic field ; and 

 it was such, when the upper part of the globe moved westward, 

 as to send the south ends of the galvanometer needles to the 

 west also : eight or ten revolutions of the globe would cause the 

 needles to pass through 80° or 90°. 



3353. The soft iron sphere was placed in the magnetic field ; 

 it was so good in character as to retain very slight traces of 

 magnetism when taken out again. Being revolved, it gave a 

 current of electricity, the same in direction as that of the 



