REPORT ON ELECTRICITY, MAGNETISM, AND HEAT. 11 
Coulomb reformed the iEpinian theory of magnetism, as he 
reformed that of electricity, by adopting the supposition of two 
fluids instead of one 5 and for the same reason, namely, that 
two south poles and tw^o north poles alike repel each other; 
which could not take place if either austral or boreal magnetism 
were a mere negation, without supposing a mutual repulsion 
common to all magnetic matter. But there was another more 
peculiar hypothesis which he found it necessary to introduce in 
addition to those of iEpinus. Several conductors placed in con¬ 
tact, end to end, make one conductor; but several pieces of iron 
so placed do not make one magnet • each piece has its own poles. 
If we cut a magnet in pieces, each piece has polarity. These 
facts forbade the supposition that the fluids which give magnetic 
polarity are transferred from one part of the iron to another; 
yet these fluids must be separated to produce the phenomena. 
Coulomb reconciles these conditions by supposing that the mag¬ 
netic body consists of small particles ; and that the fluids are 
separated in each such particle, but never pass out of it. He 
shows that in this way a line of particles would have a sensible 
magnetism at each point, arising from the excess of one mag¬ 
netism at such point over the opposite magnetism 5 and he proves 
that* “ on this hypothesis the calculation of the magnetic actions, 
or of the intensity of the magnetic forces of each point, must 
give us precisely the same result as that of the transport of the 
magnetic fluid from one extremity of a needle to another.” 
His calculations for the confirmation of this theory of mag¬ 
netism are therefore the same as those which had been requisite 
for the theory of electricity. He found such a conformity be¬ 
tween the fundamental experiments and the calculation, as gave, 
in his opinion, great weight to the systemf. Thus he ascertained 
by experiment, that in two similar saturated needles of the same 
substance, the moments of the force of terrestrial magnetism 
were as the cubes of the homologous dimensions, which agrees 
with the theory. He also found by experiment that the magnetic 
intensity at different points in a long needle was nearly as the 
distance from the centre; and by conceiving the needle as a cy¬ 
linder divided into portions, and calculating the mutual action 
of these portions J, he approximately verified this as the theo¬ 
retic law ; and he asserts generally, that § “ by the help of cer¬ 
tain corrections, it is easy to make the theory square with mag¬ 
netic phenomena.” 
Probably few persons who have studied the subject since that 
time have been disposed to deny that this theory gives the laics 
* Acad. Par. 1789, p. 492. f Ibid., p. 487. 
X Ibid., p. 485. § Ibid., p. 492. 
