very curiously, to the determination of the true diameters of the
satellites, that is to say, of small luminous points, which, with the
telescopes then in use, showed no perceptible diameter.

I will rest contented with these general considerations; only remarking,
in addition, that the diaphragms used by Bailly were not intended only
to diminish the quantity of light contributing to the formation of the
images, but that they considerably increase the diameter, and in a
variable way, at least in the instance of stars.

Under this new aspect, it will be requisite to submit the question to a
new examination.

Any geometers and astronomers who wish to know all the extent of
Bailly's labours, must not content themselves with consulting the
collections in the Academy of Sciences; for he published, at the
beginning of 1766, a separate work under the modest title of _Essay on
the Theory of Jupiter's Satellites_.

The author commences with the _Astronomical History of the Satellites_.
This history contains an almost complete analysis of the discoveries by
Maraldi, by Bradley, by Wargentin. The labours of Galileo and his
contemporaries are given with less detail and exactness. I have thought
that I ought to fill up the lacunæ, by availing myself of some very
precious documents published a few years since, and which were unknown
to Bailly.

But this I will do in a separate notice, free from all preconceived
ideas, and free from all party spirit; I will not forget that an honest
man ought not to calumniate any one, not even the agents of the