1826.] Magnetism of Metals, 8^c, arising from their Rotation, 185 



one stroke per second of the treadle of the lathe; and this 

 velocity, unless the contrary is mentioned, is to be understood 

 of all the rotations so communicated, spoken of in the remainder 

 of this account. 



The copper-plate thus revolving, the disc of copper first-men- 

 tioned was suspended over it; but though at first it seemed 

 to be very slightly affected, yet on frequent and most careful 

 repetition of the experiment, with every precaution to guard 

 against currents of air, not the most trifling effect could be 

 perceived. This remarkable result, while it stands opposed to 

 any theory of magnetic vortices generated by the rotation of 

 one body, and transferring a part of its motion to others, is, on 

 the other hand, perfectly consonant with, and indeed a necessary 

 consequence of the view which will be taken of the subject in 

 the sequel. 



In like manner a bar of hardened, but not magnetized steel, 

 was very slightly, if at all, set in rotation by the revolving 

 copper, not more than probably would correspond to the small 

 degree of magnetism unavoidably developed in it in the act of 

 hardening ; but when magnetized to saturation, it was made to 

 revolve rapidly. This experiment appears decisive as to the 

 origin of the magnetic virtue exhibited by the copper and other 

 bodies in these experiments. It is obviously induced by the 

 action of the magnetic bar, compass-needle, &c. on their 

 molecules. 



Our next inquiry was directed to the degree in which this 

 development of magnetic virtue takes place in different metals 

 and other bodies. For this purpose two different processes 

 were adopted. The first consisted in securing each of the 

 10-inch discs already spoken of, successively, on the vertical axis 

 of our machine (which was now fitted up more firmly). Giving 

 them thus a rotation in their own planes, the azimuth compass 

 above-mentioned was placed on a convenient stand centrally 

 over each at the same distance. The deviations observed, and 

 the ratios of their sines to that of the deviation produced by one 

 of them (copper) chosen as a standard, were as follows : 



Name of the re- 

 volving body. 



Copper , . 



Zinc 



Tin , 



Lead 



Antimony , 

 Bismuth . 

 Wood.... 



(Motion of 

 disc direct, or 

 screwing.) 



the(M 



lio 30' 



7 

 30 



2 50 

 1 12 



otion retro 

 grade, or un- 

 screwing.) 



11° IT 



10 15 



5 12 



2 55 



1 17 



6 







Mean. 



11° 24' 



10 11 



5 21 



2 53 



1 16 



6 







Ratio of the force 

 to that of cop- 

 per. 



1-00 

 0-90 

 0-47 

 0-25 

 O-ll 

 0-01 

 O'OO 



The experiment was repeated (some weeks afterwards), placing 



