176 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXIII.) 
2658. In the next place, if the effect were produced by induced currents in the 
mass (2642.), division of the mass would stop these currents and so alter the effect ; 
whereas if produced by a true diamagnetic polarity, division of the mass would not 
affect the polarity seriously, or in its essential nature (2430.). Some copper filings 
were therefore digested for a few days in dilute sulphuric acid to remove any adhe- 
ring iron, then well-washed and dried, and afterwards warmed and stirred in the air, 
until it was seen by the orange colour that a very thin film of oxide had formed upon 
them : they were finally introduced into a glass tube (2653.) and employed as a core. 
It produced no effect whatever, but was now as inactive as bismuth. 
2659. The copper may however be divided so as either to interfere with the 
assumed currents or not, at pleasure. Fine copper wire was cut up into lengths of 
5 ^ inches, and as many of these associated together as would form a compact cylin- 
der three-quarters of an inch in diameter (2643.) ; it produced no effect at the galva- 
nometer. Another copper core was prepared by associating together many discs of 
thin copper plate, three-quarters of an inch in diameter, and this affected the gal- 
vanometer, holding its needle 25° or 30° from zero. 
2660. I made a solid helix cylinder, three-quarters of an inch in diameter and 
2 inches long, of covered copper wire, one-sixteenth of an inch thick, and employed 
this as the experimental core. When the two ends of its wire were unconnected, 
there was no effect upon the experimental helix, and consequently none at the gal- 
vanometer ; but when the ends were soldered together, the needle was well affected. 
In the first condition, the currents, which tended to be formed in the mass of moving 
metal, could not exist because the metal circuit was interrupted ; in the second they 
could, because the circuit was not interrupted ; and such division as remained did not 
interfere to prevent the currents. 
2661. -The same results were obtained with other metals. A core cylinder of gold, 
made of half-sovereigns, was very powerful in its effect on the galvanometer. A cy- 
linder of silver, made of sixpenny pieces, was very effectual ; but a cylinder made of 
precipitated silver, pressed into a glass tube as closely as possible, gave no indications 
of action whatever. The same results were obtained with disc cylinders of tin and 
lead, the effects being proportionate to the condition of tin and lead as bad con- 
ductors (2655.). 
2662. When iron was divided, the effects were exactly the reverse in kind. It was 
necessary to use a much coarser galvanometer and apparatus for the purpose ; but 
that being done, the employment of a solid iron core, and of another of the same size 
or weight formed of lengths of fine iron wire (2659.), showed that the division had 
occasioned no inferiority in the latter. The excellent experimental researches of 
Dove* on the electricity of induction, will show that this ought to be the case. 
2663. Hence the result of division in the diamagnetic metals is altogether of a 
nature to confirm the conclusion, that the effects produced by them are due to in- 
* Taylor’s Scientific Memoirs, v. p. 129. I do not see a date to the paper. 
