observed, also whatever be the distance from that body to the sun, or to the planet; finally, whatever be the sensibility of the observer’s sight, all which circumstances considerably influence the time of apparent disappearance.  The same series of ingenious and delicate observations led the author, 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 lacunae, 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.

BAILLY’S LITERARY WORKS.—­HIS BIOGRAPHIES OF CHARLES V.—­OF LEIBNITZ—­OF PETER CORNEILLE—­OF MOLIERE.

When Bailly entered the Academy of Sciences, the perpetual secretary was Grandjean de Fouchy.  The bad health of this estimable scholar occasioned an early vacancy to be foreseen.  D’Alembert cast his views on Bailly, hinted to him the survivorship to Fouchy, and proposed to him, by way of preparing the way, to write some biographies.  Bailly followed the advice of the illustrious geometer, and chose as the subject of his studies, the eloges proposed by several academies, though principally by the French Academy.