152 DOVE ON THE ELECTRICITY OF INDUCTION. 



according to the manner in which the substances were made 

 moveable, namely, either by swimming upon water or quicksil- 

 ver by means of pieces of cork, or by suspension on threads 

 possessing very little torsion. 



The method which I have pursued is however different. I 

 have tested the relative magnetizabiUty of the different metals 

 by the electric currents induced by them in a spirally coiled 

 conducting w ire surrounding them, when the magnetism excited 

 in them became evanescent. How far the results obtained in 

 this manner agree with the observations of former natural philo- 

 sophers, will be best seen after a short notice of their results has 

 here been given. 



63. According to Brugmans *, lead, tin, antimony, gold and 

 silver possess no magnetic power ; on the contrary, copper float- 

 ing on water or mercury is slightly attracted, zinc more power- 

 fully, as is also bismuth that has a white shining silver colour, 

 whilst bismuth having a dark, nearly violet colour is repelled by 

 both poles of the magnet. Cobalt exhibits a very weak attrac- 

 tion, and arsenic none at all ; on the contrary, poles and a point 

 of neutrality can be produced in brass. Lehmannf endeavoured 

 at great length to prove that the magnetism of brass was attri- 

 butable to iron mixed with it; whilst, on the contrary, CavalloJ 

 came to a contrary conclusion as the result of his own experi- 

 ments. Brugmans considers attraction by the magnet as a proof 

 of the presence of associated iron. 



Coulomb § caused needles of gold, silver, lead, copper and tin, 

 7 millimetres long, and weighing 40 milligrammes, to oscillate 

 between the opposite poles of a powerful magnet, and found the 

 time requisite for four oscillations to be respectively 22", 20", 

 18", 22", 19", whilst, when removed from the influence of the 

 magnet, each required 44" to complete four oscillations. On 

 the repetition of Coulomb's experiments in the Royal Institu- 

 tion, Thomas Young obtained less marked results than Coulomb. 

 Coulomb himself showed, by artificial combinations of iron 

 filings M'ith wax, how little iron was requisite to produce similar 

 indications. Biot|| considers the alternative, that these phasno- 



* Magnetismiis, sen de affinitatibus nwgneticis ohservationes AcadeniiccE, 

 1778, 4. 



t De ciipro et or'ichalco mafj7ietico, Nov. Com. Petr. xii. p. 368. 



I Treatise on Magnetism, 1787, p. 283. 



§ Journal de Physique, liv. pp. 307, 4.54, 1802. 



II Precis Eleme7ifaire de Physique, sec. ed. ii. p. 78. 



