REPORT ON ELECTRICITY, MAGNETISM, AND HEAT. 
5 
he calculates the relative quantities of electricity which will exist 
at the surfaces of each of 25 spheres, placed in a straight line, 
by elimination among the requisite number of equations*. 
In this manner Coulomb obtains theoretical results correspond¬ 
ing to a great number of experiments carefully made and ex¬ 
tremely varied in their circumstances. The agreement of the 
theoretical with the experimental numbers is not exact; which 
indeed could not be expected, since the former are only approxi¬ 
mations, and the latter are affected by unavoidable errors. But 
an agreement appeared in the general scale and proportion of the 
numbers which shows that the theory gave in all cases the true 
quantity either exactly or very nearly; and this was further 
confirmed by the consideration of extreme cases, as pointed con¬ 
ductors, long conducting strings, and the like. Cases including 
long wires and plates had also been calculated by Cavendish, 
and found to agree in their general features with experiments. 
It should be observed also that Coulomb, at the very outset of 
his researches, had begun by ascertaining experimentally the for¬ 
mulae by which allowance was to be made for two main causes 
of error, the dispersion of electricity from electrised bodies into 
the air, and its escape along the supports which were intended 
to insulatef. I conceive that if the results of the theory and 
of experiment, as stated in Coulomb’s six memoirs on electri¬ 
city X, were collected in parallel columns, the amount of evidence 
would be considered as quite sufficient to prove that the theory 
gave at least good approximate laws of the phenomena in a large 
class of cases of the distribution of electricity ; and adding to 
these the previous agreement obtained by Cavendish, this merit 
might be claimed for it through almost the whole range of ob¬ 
vious cases. 
I do not think Coulomb has anywhere, after thus establish¬ 
ing the truth of his formulae, summed up the evidence, and given 
his own view of the degree of certainty of the theory. In his 
6th memoir on electricity §, he speaks of the two theories of one 
and of two electric fluids, and adds, ‘ e As these two explanations 
have only a greater or less degree of probability, I warn the 
reader, in order to put the following theory out of the reach of 
all systematic dispute, that in the supposition of two electric 
fluids I have no other intention than to present the results of 
calculation and of experiment with the smallest possible number 
of elements, and not to indicate the true cause of electricity. 
I shall reserve for the end of my labours on electricity the exa- 
* Acad. Par. 1788, p. 611. 
X Acad. Par. 1785—1788. 
f 3rd memoir, Acad. Par. 1785, p. 612, 
§ Acad. Par. 1788, p. 673. 
