ON THE POLARITY OF THE DIAMAGNETIC FORCE. 
257 
Deeming that the magnetism of the cores of silver was due to magnetic impurity 
attaching itself to the paper which covered them, a number of fourpenny pieces were 
procured, washed in ammonia and water, and enclosed in thin glass tubes. The fol- 
lowing were the results : — 
XXX. 
Silver cylinders (fourpenny pieces). 
Current direct. 
Position 1 . 490 
Position 2. 565 
Position 3. 660 
Here also we have a very considerable action indicative of magnetic polarity. On 
examining the cylinders between the poles of an electro-magnet, they were found 
decidedly magnetic. This, therefore, appears to be the common character of our 
silver coins. The tubes which contained the pieces were sensibly neutral. 
Knowing the difficulty of demonstrating the existence ot diamagnetic polarity in 
ordinary insulators, M. Matteucci suggested that insulated fragments of bismuth 
ought to be employed, the insulation being effected by a coat of lac or resin. I con- 
structed a pair of cylinders in accordance with the suggestion of M. Matteucci. 
The following are the results they yielded with a direct current : — 
XXXI. 
Position 1. 730 
Position 2. 750 
Position 3. 768 
Here we have a very marked action, but the polarity indicated is magnetic polarity. 
On subsequent examination, the cylinders proved to be magnetic. This was due to 
impurities attaching themselves to the resin. 
But the resin may be done away with and the powdered metal still rendered an 
insulator. This thought was suggested to me by an experiment of Mr. Faraday, 
which I will here describe. Referring to certain effects obtained in his investiga- 
tions on supposed diamagnetic polarity, he writes thus : — ‘‘ If the effect were produced 
by induced currents in the mass, 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. Some 
copper filings were therefore digested for a few days in dilute sulphuric acid to remove 
any adhering 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 and employed as 
a core. It produced no effect whatever, but was as inactive as bismuth.” (Exper. 
Resear. 2658.) 
