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Astronomical and Nautical Collections. 319 
given state of magnetic or electric properties which they have been 
made to assume. With regard to electricity, the bodies called 
conductors are instantly electrified by the influence of neighbouring 
bodies already electrified, and when this influence is removed, they 
no longer retain any trace of electricity. Nonconducting bodies, 
on the contrary, are not sensibly electrified by this influence, ex- 
cept when it is very powerful or very long continued ; but when 
they have once been electrified by any other means, they preserve, 
at each point, the electricity which has been once established in it, 
retaining it by a peculiar power of the matter of which they are 
composed. In this respect, such bodies, as are capable of mag- 
netism, present us with a similar diversity; some of them, as soft 
iron, for example, which has neither been twisted nor screwed, are 
rendered magnetic by the influence of a neighbouring magnet ; and 
when they are removed from it, they no longer exhibit any signs of 
magnetism: others, such as hard steel, are very little susceptible 
of this temporary influence ; but if magnetism has been once ex- 
cited in them by more powerful means, they preserve this state of 
magnetism, and, without doubt, by virtue of some particular 
action which their particles exert on the boreal and austral 
fluids. 
Such are the principal analogies that are readily observed be- 
tween electricity and magnetism ; but on the other hand, there ex- 
ist between these two affections of bodies some essential differences 
which must be mentioned, and which prevent the immediate ap- 
plication of the theory of electricity to the phenomena of mag- 
netism, 
Electricity affects all bodies, whether as passing freely through 
them, or as being attached to their particles: on the contrary, there 
are only a small number of bodies, such*as iron in its different 
states, steel, nickel, and cobalt, in which distinct traces of magnetic 
action have been observed. Hence it has become a question, whe- 
ther magnetism is a particular fluid, found only in bodies suceptible 
of its influence, of if it is merely a modification of the electric fluid, 
distributed in a particular manner. This question can scarcely be 
decided in the present state of the science ; all that has hitherto been 
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