SUPPOSED POLARITY OF DIAMAGNETIC BODIES. 
181 
than before, being now at a maximum, but in the same order ; as regarded antimony 
and bismuth, they were very small, amounting to not more than half a degree, and may 
very probably have been due to a remainder of irregular action in some part of the 
apparatus. All the experiments with the divided cores (2658, &c.) were repeated with 
the same results as before. Phosphorus, sulphur and gutta percha did not, either 
in this or in the former state of the commutator, give any indication of effect at the 
galvanometer. 
26/9. As an illustration of the manner in which this position of the commutator 
caused a separation of the effects of copper and iron, I had prepared a copper cylinder 
core 2 inches in length having an iron wire in its axis, and this being employed 
in the apparatus gave the pure effect of the copper with its induced currents. Yet 
this core, as a whole, was highly magnetic to an ordinary test-needle ; and when the 
two changes of the commutator were not equidistant from the one stop or the other 
(2670. 2677-)) effect came out powerfully, overruling the former and pro- 
ducing very strong contrary deflections at the needle. The platinum core which I 
have used is an imperfect cylinder, 2 inches long and 0'62 of an inch thick : it points 
magnetically between the poles of a horseshoe electro-magnet (2381.), making a 
vibration in less than a second, but with the above condition of the commutator 
(2675.) gives 4° of deflection due to the induced currents, the magnetic effect being 
annulled or thrown out. 
2680. Some of the combined effects produced by oblique position of the commu- 
tator points were worked out in confirmation of the former conclusions (26770* 
When the commutator was so adjusted as to combine any polar power which the 
bismuth, as a diamagnetic body, might possess, with any conducting power which 
would permit the formation of currents by induction in its mass (2676.), still the 
effects were so minute and uncertain as to oblige me to say that, experimentally, it 
is without either polar or inductive action. 
2681. There is another distinction which may usefully be established between the 
effects of a true sustainable polarity, either magnetic or diamagnetic, and those of 
the transient induced currents dependent upon time. If we consider the resistance 
in the circuit, which includes the experimental helix and the galvanometer coil, as 
nothing, then a magnetic pole of constant strength passed a certain distance into 
the helix, would produce the same amount of current electricity in it, whether the 
pole were moved into its place by a quick or a slow motion. Or if the iron core be 
used (2668.) the same result is produced, provided, in any alternating- action, the 
core is left long enough at the extremities of its journey to acquire, either in its 
quick or slow alternation, the same state. This I found to be the fact when no com- 
mutator nor dominant magnet was used ; a single insertion of a weak magnetic pole 
gave the same deflection, whether introduced quickly or slowly; and when the resi- 
dual dominant magnet, an iron wire core, and the commutator in its position a, h 
(2677-) were used, four journeys to and from produced the same effect at the galva- 
nometer when the velocities were as 1 ; 5 or even as 1 : 10. 
