OF NATURAL PHILOSOPHY. 32i 



(36.) Iron, and its oxides and alloys, were for a 

 long time the only substances considered susceptible 

 of magnetism. The loadstone was even one of the 

 examples produced by Bacon of that class of phy- 

 sical instances to which he applies the term "In- 

 stantiae monodicae" singular instances. And the 

 history of magnetism affords a beautiful comment on 

 his remark on instances of this sort. " Nor should 

 our enquiries, " he observes, " into their nature be 

 broken off, till the properties and qualities found in 

 such things as may be esteemed wonders in nature 

 are reduced and comprehended under some certain 

 law ; so that all irregularity or singularity may be 

 found to depend upon some common form, and the 

 wonder only rest in the exact differences, degrees, 

 or extraordinary concurrence, and not in the species 

 itself." The discovery of the magnetism of nickel ^ 

 which though inferior to that of iron, is still con- 

 siderable ; that of cobalt, yet feebler, and that of 

 titanium, which is only barely perceptible, have 

 effectually broken down the imaginary limit between 

 iron and the other materials of the world, and esta - 

 Wished the existence of that general law of conti- 

 nuity which it is one chief business of philosophy 

 to trace throughout nature. The more recent dis- 

 coveries of M. Arago (mentioned in 160.) have 

 completed this generalization, by showing that there 

 is no substance but which, under proper circum- 

 stances, is capable of exhibiting unequivocal signs of 

 the magnetic virtue. And to obliterate all traces of 

 that line of separation which was once so broad, we 

 are now enabled, by the great discovery of Oersted, 

 to communicate at and during pleasure to a coiled 

 v 3 



