The subsequent year I see him associated with Lacaille in observing the transit of Venus over the sun's disk. It was an extraordinary piece of good fortune, Gentlemen, at the very commencement of his scientific life, to witness in succession two of the most interesting astronomical events: the first predicted and well established return of a comet; and one of those partial eclipses of the sun by Venus, that do not recur till after the lapse of a hundred and ten years, and from which science has deduced the indirect but exact method, without which we should still be ignorant of the fact that the sun's mean distance from our earth is thirty-eight millions of leagues. I shall have completed the enumeration of Bailly's astronomical labours performed before he became an academician, when I have added, from observations of the comet of 1762, the calculation of its parabolic orbit; the discussion of forty-two observations of the moon by La Hire, a detailed labour destined to serve as a starting point for any person occupying himself with the lunar theory; finally, also the reduction of 515 zodiacal stars, observed by Lacaille in 1760 and 1761. FOOTNOTE: [6] This long list of supposed difficulties in making an exact observation is hardly worthy of a zealous astronomer. Our author shows no enthusiasm for his subject here, and ends by ascribing the whole jeremiad to Lacaille, a man of very great practical perseverance. It is to be regretted that Arago never refers to observations of his own, but constantly quotes from others, nor does he always select the best. --_Translator's Note_. BAILLY A MEMBER OF THE ACADEMY OF SCIENCES.--HIS RESEARCHES ON JUPITER'S SATELLITES. Bailly was named member of the Academy of Sciences the 29th January, 1763. From that moment his astronomical zeal no longer knew any bounds. The laborious life of our fellow-academician might, on occasion, be set up against a line, more fanciful than true, by which an ill-natured poet stigmatized academical honours. Certainly no one would say of Bailly, that after his election, "Il s'endormit et ne fit qu'un somme." "He fell asleep and made but one nap (or sum)." On the contrary, we cannot but be surprised at the multitude of literary and scientific labours that he accomplished in a few years. Bailly's earliest researches on Jupiter's satellites began in 1763.