Magneto-E lectricity, and Electro-magnetical Machines. 131 
that subject more particularly, and find the generalization may 
be extended still further, and include all electro-magnetical 
motion produced by two magnets, or by a conductor and a mag- 
net. It may then be stated as follows: If a galvanic current 
from a battery produces an electro-maguetical motion in any piece 
of apparatus, and that battery be detached and a galvanometer 
substituted in its place, and connected with the same wire or 
poles of the apparatus ; then, on compelling the same motion in 
the apparatus by hand or otherwise, the galvanometer will be 
deflected, showing a current of magneto-electricity in a direction 
opposite to that current from the battery which had produced the 
same motion. I have tried the experiment with Barlow’s “revolv- 
ing star,”’* the “revolving wire” of Mr. Faraday, the “ revolving 
cylinder,” with Andrews’ revolving magnet, De La Rive’s coil, 
and also with one galvanometer acting upon another. 
The revolving magnet is the most simple magneto-electric 
machine possible. Take a cylindrical straight bar magnet, and 
holding two wires from the galvanometer, one in contact with 
one end of the magnet, and the other in contact with the mid- 
dle, let an assistant twist the magnet round on its axis, the wires 
slipping on its surface ; the galvanometer will immediately indi- 
cate the production of magneto-electricity. Or, the lower end 
of the magnet may be sharpened into a sort of pivot, and be 
pressed by the breast down into an indentation in one of the 
conductors, while the contact at the middle and the rotation of 
the bar are performed without anassistant. With a magnet eight 
inches long, and one sixth of an inch in diameter, made of watch- 
maker’s wire, nicely pivoted, and turned by drawing the finger 
across it, I obtained a deflection of my twelve inch galvanometric 
needle of sixty six degrees, viz. from N. 45 E. to N. 21 W. It 
is evident that the galvanometer itself is included in this rule. I 
connected my large thermoscopic galvanometer, by long wires, 
with the poles of an elegant and delicate Mellonian galvanometer, 
and then put the needle of the larger one into rotary motion by 
hand. ‘The needle of the smaller instrument was deflected quite 
to the west, while the needle of the larger swept one half of its 
* This This experiment is identical in principle with the ago of Mr. Faraday, the 
apparatus for which is figured in Brande’s Chem. 1836, p 
