SUPPOSED POLARITY OF DIAMAGNETIC BODIES. 
177 
duced currents moving; through their masses, and not to any polarity correspondent 
in its general nature (though opposed in its direction) to that of iron. 
2664 . In the third place ( 2656 .), another and very important distinction in the ac- 
tions of a diamagnetic metal may be experimentally established according as they 
may be due either to a true polarity, or merely to the presence of temporary induced 
currents ; and as for the consideration of this point diamagnetic and magnetic pola- 
rity are the same, the point may best be considered, at present, in relation to iron. 
2665 . If a core of any kind be advanced towards the dominant magnet and with- 
drawn from it by a motion of uniform velocity, then a complete journey or to and 
from action might be divided into four parts ; the to^ the stop after it ; the from, and 
the stop succeeding that. If a core of iron make this journey, its end towards the 
dominant magnet becomes a pole, rising in force until at the nearest distance, and 
falling in force until at the greatest distance. Both this effect, and its progression 
inwards and outwards, cause currents to be induced in the surrounding helix, and 
these currents are in one direction as the core advances, and in the contrary direction 
as it recedes. In reality, however, the iron does not travel with a constant velocity ; 
for, because of the communication of motion from a revolving crank at the machine 
( 2643 .), it, in the to part of the journey, gradually rises from a state of rest to a maxi- 
mum velocity, which is half-way, and then as gradually sinks to rest again near the 
magnet : — and the from part of the journey undergoes the same variations. Now as 
the maximum effect upon the surrounding experimental helix depends upon the velo- 
city conjointly with the intensity of the magnetic force in the end of the core, it is 
evident that it will not occur with the maximum velocity, which is in the middle of 
the to or from motion ; nor at the stop nearest to the dominant magnet, where the 
core end has greatest magnetic force, but somewhere between the two. Nevertheless, 
during the whole of the advance, the core will cause a current in the experimental 
helix in one direction, and during tlie whole of the recession it will cause a current 
in the other direction. 
2666 . If diamagnetic bodies, under the influence of the dominant magnet, assume 
also a polar state, the difference between them and iron being only that the poles of 
like names or forces are changed in place ( 2429 . 2430 .), then the same kind of action 
as that described for iron would occur with them ; the only difference being, that the 
two currents produced would be in the reverse direction to those produced by iron. 
2667. If a commutator, therefore, were to be arranged to gather up these currents, 
either in the one case or the other, and send them on to the galvanometer in one 
consistent current, it should change at the moments of the two stops ( 2665 .), and 
then would perform such duty perfectly. If, on the other hand, the commutator 
should change at the times of maximum velocity or maximum intensity, or at two 
other times equidistant either from the one stop or from the other, then the parts of 
the opposite currents intercepted between the changes would exactly neutralize each 
other, and no final current w’ould be sent on to the galvanometer. 
MDCCCL. 2 A 
