SUPPOSED POLARITY OF DIAMAGNETIC BODIES. 
179 
raotion ; and these would be at their maximum force just before and just after the to 
or inner stop, for then the copper would be in the most intense parts of the magnetic 
field. The rising current of the copper core for the in portion of the journey would 
produce a current in one direction in the experimental helix, the stopping of the copper 
and consequent falling of its current would produce in the experimental helix a current 
contrary to the former ; the first instant of motion outwards in the core would produce 
a maximum current in it contrary to its former current, and producing in the experi- 
mental helix its inductive result, being a current the same as the last there produced; 
and then, as the core retreated, its current would fall, and in so doing and by its final 
stop, would produce a fourth current in the experimental helix, in the same direction 
as the first. 
2672. The four currents produced in the experimental helix alternate by twos, i.e. 
those produced by the falling of the first current in the core and the rising of the 
second and contrary current, are in one direction. They occur at the instant before 
and after the stop at the magnet, i. e. from the moment of maximum current (in the 
core) before, to the moment of maximum current after, the stop; and if that stop is 
momentary, they exist only for that moment, and should during that brief time be 
gathered up by the commutator. Those produced in the experimental helix during 
the falling of the second current in the core and the rising of a third current (iden- 
tical with the first) in the return of the core to the m.agnet, are also the same in 
direction, and continue from the beginning of the retreat to the end of the advance 
(or from maximum to maximum) of the core currents, i. e. for almost the whole of the 
core journey; and these, by its change at the maximum moments, the commutator 
should take up and send on to the galvanometer. 
2673. The motion however of the core is not uniform in velocity, and so, sudden 
in its change of direction, but, as before said (2665.), is at a maximum as respects 
velocity in the middle of its approach to and retreat from the dominant magnet ; and 
hence a very important advantage. For its stop may be said to commence immediately 
after the occurrence of the maximum velocity; and if the lines of magnetic force were 
equal in position and power there to what they are nearer to the magnet, the con- 
trary currents in the expei’imental helix would commence at those points of the jour- 
ney ; but, as the core is entering into a more intense part of the field, the current in 
it still rises though the velocity diminishes, and the consequence is, that the maxi- 
mum current in it neither occurs at the place of greatest velocity, nor of greatest 
force, but at a point between the two. This is true both as regards the approach and 
the recession of the core, the two maxima of the currents occurring at points equi- 
distant from the place of rest near the dominant magnet. 
2674. It is therefore at these two points that the commutator should change, 
if adjusted to produce the greatest effect at the galvanometer by tlie currents excited 
in the experimental helix, through the influence of, or in connection with, currents 
of induction produced in the core ; and experiment fully justifies this conclusion. 
2 A 2 
