172 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXIII.) 
to indicate that the differences between these modes of action and that of a real pola- 
rity, whether magnetic or diamagnetic, might serve as a foundation on which to base 
a mode of investigation, and also to construct an apparatus that might give useful 
conclusions and results in respect of this inquiry. For, if the polarity exists it must 
be in the particles and for the time permanent, and therefore distinguishable from 
the momentary polarity of the mass due to induced temporary currents ; and it 
must also be distinguishable from ordinary magnetic polarity by its contrary direc- 
tion. 
2643. A straight wooden lever, 2 feet in length, was fixed by an axis at one end, 
and by means of a crank and wheel made to vibrate in a horizontal plane, so that its 
free extremity passed to and fro through about 2 inches. Cylinders or cores of metal 
or other substances, 5^ inches long and three-quarters of an inch diameter, were fixed 
in succession to the end of a brass rod 2 feet long, which itself was attached at the 
other end to the moving extremity of the lever, so that the cylinders could be moved 
to and fro in the direction of their length through the space of 2 inches. A large 
cylinder electro-magnet was also prepared (2191.), the iron core of which was 21 inches 
long and 1'7 inch in diameter; but one end of this core was made smaller for the 
length of 1 inch, being in that part only 1 inch in diameter. 
2644. On to this reduced part was fixed a hollow helix consisting of 516 feet of fine 
covered copper wire : it was 3 inches long, 2 inches external diameter, and 1 inch 
internal diameter : when in its place, 1 inch of the central space was occupied by the 
reduced end of the electro-magnet core which carried it ; and the magnet and helix 
were both placed concentric with the metal cylinder above mentioned, and at such a 
distance that the latter, in its motion, would move within the helix in the direction of 
its axis, approaching to and receding from the electro-magnet in rapid or slow suc- 
cession. The least and greatest distances of the moving cylinder from the magnet 
during the journey were one-eighth of an inch and 2*2 inches. The object of course 
was to observe any influence upon the experimental helix of fine wire which the metal 
cylinders might exert, either whilst moving to or from the magnet, or at different 
distances from it*. 
2645. The extremities of the experimental helix wire were connected with a very 
delicate galvanometer, placed 18 or 20 feet from the machine, so as to be unaffected 
directly by the electro-magnet; but a commutator was interposed between them. 
This commutator was moved by the wooden lever (2643.), and as the electric currents 
which would arrive at it from the experimental helix, in a complete cycle of motion 
or to and fro action of the metal cylinder (2643.), would consist of two contrary por- 
tions, so the office of this commutator was, sometimes to take up these portions in 
succession and send them on in one consistent current to the galvanometer, and at 
* It is very probable that if the metals were made into cylinders shorter, but of larger diameter than those 
described above, and used with a corresponding wider helix, better results than those I have obtained would 
be acquired. 
