repetition of M Arago's experiments on magnetism, ^c. 41 1 
When the poles of the revolving magnet were comiected 
by a piece of soft iron, the rotation of the copper disc was in 
like manner almost entirely annihilated. 
6 . Resuming now the original form of the experiment, 
the copper disc of lo inches diameter and -j inch thick, was 
placed on the vertical axis, and made to revolve with a velo- 
city of 7 turns in a second, a velocity which it was found 
convenient to give, and easy to maintain, corresponding as it 
did with 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. 
7. The copper plate thus revolving, the disc of copper 
mentioned in Art. 2 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. 
8 . In like manner a bar of hardened, but not magnetised 
steel, was very slightly, if at all, set in rotation by the re- 
volving copper, not more than probably would correspond to 
the small degree of magnetism unavoidably developed in it 
in the act of hardening ; but when magnetised to saturation, 
it was made to revolve rapidly. This experiment appears 
decisive as to the origin of the magnetic virtue exhibited by 
