30 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXVIII.) 
Two clips, as at C, hold the ends of the galvanometer wire (also of copper) ; and the 
latter are made to press against the rings by their elasticity, and give an effectual 
contact bearing, which generates no current, either by difference of nature or by 
friction, during the revolution of the axis. 
3085. The two magnets are bars, each 12 inches long, 1 inch broad, and 0*4 of 
an inch thick. They weigh each 19 ounces, and are of such a strength as to lift each 
other end to end and no more. When the two are adjusted in their place, it is 
with the similar poles together, so that they shall act as one magnet, with a division 
down the middle : they are retained in their place by tying, or, at times, by a ring of 
copper which slips tightly over them and the axis. 
3086. The galvanometer is a very delicate instrument made by Ruhmkorff (2651 .). 
It was placed about 6 feet from the magnet apparatus, and was not affected by any 
revolution of the latter. The wires, connecting it with the magnets, were of copper, 
0’04 of an inch in diameter, and in their whole length about 25 feet. The length of 
the wire in the galvanometer 1 do not know ; its diameter was of an inch. The 
condition of the galvanometer, wires, and magnets, was such, that when the bend of 
the wires was formed into a loop, and that carried once over Fig. 2. 
the pole of the united magnets, as from a to h, fig. 2, the gal- « 
vanometer needle was deflected two degrees or more. The 
vibration of the needle was slow, and it was easy therefore to 
reiterate this action five or six times, or oftener, breaking and 
making contact with the galvanometer at right intervals, so as 
to combine the effect of like induced currents; and then a de- 
flection of 10° or 15° on either side of zero could be readily 
obtained. The arrangement, therefore, was sufficiently sensible for first experiments; 
and though the resistance opposed by the thin long galvanometer wire to feeble 
currents was considerable, yet it would always be the same, and would not interfere 
with results, where the final effect was equal to 0°, nor in those where the conse- 
quences were shown, not by absolute measurement, but by comparative differences. 
3087- The first practical result produced by the apparatus described, in respect of 
magneto-electric induction generally, is, that a piece of metal or conducting matter 
which moves across lines of magnetic force, has, or tends to have, a current of elec- 
tricity produced in it. A more restricted and precise expression of the full effect is 
the following. If a continuous circuit of conducting matter be traced out, or con- 
ceived of, either in a solid or fluid mass of metal or conducting matter, or in wires 
or bars of metal arranged in non-conducting matter or space ; which being moved, 
crosses lines of magnetic force, or being still, is by the translation of a magnet 
crossed by such lines of force; and further, if, by inequality of angular motion, or 
by contrary motion of different parts of the circuit, or by inequality of the motion in 
the same direction, one part crosses either more or fewer lines than the other ; then 
a current will exist round it, due to the differential relation of the two or more inter- 
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