MAGNETIC CHARACTERS OF METALS, &c. 637 
indeed, be the sole cause of any motions that may 
happen to be observed. Moreover, a delicate 
magnetic needle does not possess a sufficient 
degree of power to bring into play the minute 
portions of magnetism that lie dormant in many 
bodies. These exiguous sleeping forces can 
never be roused into a state of activity, and, 
consequently, can never be discevered by merely 
presenting the bodies in which they reside to the 
pole of a feeble magnetic needle. To accomplish 
their discovery a comparatively powerful magnetic 
action is absolutely required; for, when thus 
assailed, their polarization is more easily enforced, 
and their detection almost certain. The magnetic 
needle, however, may be usefully employed in 
cases where the suspected magnetism of a body 
is of some easily detected amount ; and it may be 
resorted to with advantage, in preliminary trials, 
under all circumstances, because of the possibility 
of the specimen under examination possessing a 
sufficient amount of magnetism to be detected by 
it, and the more tedious modes of inquiry being 
thus rendered unnecessary. 
16. I have found that a convenient and eftica- 
cious mode of examining bodies the magnetic 
actions of which are very feeble, and others 
4P 
