10 
FIFTH REPORT— 1835. 
be easy to trace by calculation the consequences of the theory. 
Even what might appear very simple problems, as the distribu¬ 
tion of the fluid on rectangular plates, have not, so far as I am 
aware, been solved mathematically, and therefore we cannot im¬ 
mediately compare Mr. Harris’s experimental results in such 
cases with the theory. But we may observe a general difference 
in the mode of measuring the intensity of the action in these 
experiments from those of Coulomb. In Coulomb’s apparatus 
the energy of the electric action was estimated by the mutual 
force which is exerted between two insulated particles; in 
Mr. Harris’s researches the conducting body, whose intensity is to 
be examined, and the other conductor which it attracts or repels, 
are, one or both of them, uninsulated, or at least connected with 
a large extraneous conducting surface. This arrangement would 
make peculiar calculations requisite. In their more obvious re¬ 
sults, however, Mr. Harris’s experiments confirm the Coulom- 
bian theory: thus, it is shown * that the force of electrical at¬ 
traction is inversely as the square of the distance. Also the rule 
which Mr. Harris obtained, and which appears to have surprised 
him, that the intensity of the force measured in his way is as 
the square of the quantity of electricity, is a consequence of the 
effect of induction on the uninsulated conductor. It might be 
well worth while for some new Poisson to examine the rest of 
Mr. Harris’s results in their bearing upon the Coulombian the¬ 
ory ; although, as has been said, there would be considerable 
mathematical difficulties in the course of such a comparison. 
Magnetism .—If we now pass to the consideration of Magne¬ 
tism, we have, to a considerable extent, to repeat the same story 
which we have had to tell respecting Electricity. The attrac¬ 
tions and repulsions of magnets, their polarity, the transient 
magnetism of soft iron, led to the assumption of magnetic fluids, 
one, acting in excess or defect, or two, an austral and a boreal, 
moveable in soft iron, but fixed in hard steel 5 and thus, as in 
the case of electricity, the facts of attraction, repulsion, induced 
magnetism, could be pretty completely represented. iEpinus 
worked out mathematically the consequences of the assumption 
of one fluid, in the same work in which he performed the same 
part for electricity f. Coulomb reformed this theory, having 
in the first place X established that the force of the particles of 
the fluid is inversely as the square of the distance; a law which 
Lambert and Mayer § had already discovered, and which was 
subsequently confirmed by Barlow and Hansteen. 
* Phil. Trans. 1834. Part II. p. 238. 
f Tentamen Theories Electricitatis et Magnetismi. 1759. 
| Acad. Par. 1784. § Biogr. Univ art. Coulomb. 
