Experiments and Obfervations . 75 
degree, as it had done the fxrffc time. However, it muft be ob- 
ferved, that the pieces of platina having been rendered flat and 
thin by the firft hammering, could not be fo eafily ftruck, nor 
fpread much more, by the fecond. 
If it is true, as thofe experiments feem to prove beyond a 
doubt, that magnetifm may exift, or may belong to other 
fubftances, independent of iron, it muft follow, that the 
attra&ion of a few particles of an unknown fubftance by the 
magnet is not a fure fign of the prefence of iron. Hence thofe 
fubftances, which hitherto have been confidered as containing 
ferrugineous particles, for no other reafon but becaufe the mag- 
net attracted a fmall quantity of them, muft be confidered as 
dubious; and the conclufion of the exiftence of iron fhould not be 
admitted, except when thofe particles, which have been fepa- 
rated by the magnet, appear to be iron by fome other trial ; 
for though it is true, that iron is always attradled by the mag- 
net, yet it does not hence follow, that whatever is attracted by 
the magnet muft: be iron. 
POSTSCRIPT. 
THE exiftence of magnetifm, or of the power of attracting 
and being attra&ed by the magnetic needle, in bodies, without 
the interference of iron or any ferrugineous matter, being a 
propofition not only new and lingular, but feemingly of im- 
portance in philofophy, the experiments which tend to confirm 
it fhould be never deemed fuperfluous, nor any poffible objection 
be left unanfwered ; hence, fince the writing of the fore- 
going paper, I have endeavoured to raife objections, and to con- 
L % ' trive 
