102 BAILLT. ;. ~ 



horizon nor the zenith. This ousht to be known, even 



<_> ' 



if it should disturb the wild reveries of two or three 

 writers, who have no scientific authority : France did 

 not possess an observatory worthy of her, nor worthy of 

 the science, and capable of rivalling the other observa- 

 tories of Europe, until within these ten or twelve years. 



The earliest observations made by Bailly, from one of 

 the windows in the upper story of the Louvre gallery 

 that looks out on the Pont des Arts, are dated in the be- 

 ginning of 1760. The pupil of Lacaille was not yet 

 twenty-four years old. Those observations relate to an 

 opposition of the planet Mars. In the same year he de- 

 termined the oppositions of Jupiter and of Saturn, and 

 compared the results of his own determinations with the 

 tables. 



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 wit- 

 ness in succession two of the most interesting; astronomi- 



c* 



cal 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 hun- 

 dred 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 start- 



