“ which scarcely admit a doubt that the planet Herschel was seen by Mayer in the year 1756. and was considered by him as one of the Zodiacal stars, and as such arranged in his catalogue, being the 964 ^th. which he describes. this 964 ^th. of Mayer has been since missing, and the calculations for the planet Herschel shew that it should have been at the time of Mayer’s observation where he places his 964 ^th. star. the volume of 1787. gives you Mayer’s Catalogue of the Zodiacal stars. the researches of the Natural philosophers of Europe seem mostly in the field of chemistry, & here principally on the subjects of air & fire. the analysis of these two subjects presents to us very new ideas . . . ”

On August 20 in the same year he wrote to John Page: “ . . . I shall send you with this, if I can, & if not, then by the first good conveiance the Connoissance de tems for the years 1786. & 1787. being all as yet published. you will find in these the tables for the planet Herschel as far as the observations hitherto made admit them to be calculated. you will see also that Herschel was only the first astronomer who discovered it to be a planet, & not the first who saw it. Mayer saw it in the year 1756. and placed it in the catalogue of his Zodiacal stars, supposing it to be such. A Prussian astronomer in 1781. observed that the 964 ^th. star of Mayer’s catalogue was missing, and the calculations now prove that at the time Mayer saw his 964 ^th. star, the planet Herschel should have been precisely in the place where he noted that star . . . ”

Similarly on October 2, he sent to Rev. J. Madison of William and Mary College a number of books including the Connoissance des Temps, and explained: “ . . . In the last volume of the Conn. des tems you will find the tables for the planet Herschel. it is a curious circumstance that this planet was seen 30 years ago by Mayer, and supposed by him to be a fixed star. he accordingly determined a place for it in his catalogue of the Zodiacal stars, making it the 964 ^th. of that catalogue. Bode of Berlin observed in 1781 that this star was missing. subsequent calculations of the motion of the planet Herschel shows that it must have been, at the time of Mayer’s observation, where he had placed his 964 ^th. star . . . ”

Jefferson at various times in his correspondence showed his familiarity with the Connoissance des Temps. In the letter to Melatiah Nash for instance with suggestions for his Ephemeris , dated from Monticello November 15, 1811, Jefferson wrote: “ . . . this table [i.e. of the sun’s declination] is to be found in many astronomical books, as, for instance, in Wakeley’s Mariner’s compass rectified, and more accurately in the Connoissance des tems for 1788. it would not occupy more than two pages at the end of the work & would render it an Almanac for every part of the US.

" To give novelty, and increase the appetite for continuing to buy your Ephemeris annually, you might every year select some one or two useful tables which many would wish to possess & preserve. these are to be found in the Requisite tables, the Connoissance des tems of different years, and many in Pike’s arithmetic . . . ”

The Connoissance des Temps, the French nautical almanac, was first issued in 1696. It had received letters patent from the king, Louis XIV, on March 24, 1679.