MATHEMATICAL STUDIES. 105 
diameters of the satellites, that is to say, of small lumi- 
nous 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 vari- 
able 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 them- 
selves 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 The- 
ory of Jupiter’s Satellites. 
The author commences with the Astronomical History 
of the Satellites. This history contains an almost com- 
plete analysis of the discoveries by Maraldi, by Bradley, 
by Wargentin. ‘The labours of Galileo and his contem- 
poraries are given with less detail and exactness. I have 
thought that I ought to fill up the lacune, 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 Inquisition. 
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