1835.] First Astroiwmer-RoyuL 409 



soon after, declared that from their observations they had 

 found the same. Whether they will give such exactness, I 

 leave to those who are skilful in these things to determine. 



It was this year that the French sent Monsieur Richer to 

 observe the southern fixed stars at Cayenne ; where he also 

 observed this transit of Mars amongst the three fixed stars 

 in the water of Aquarius. His observations are printed i^n 

 the Voyages Astronomiques ; from whence I have transcribed 

 them to be printed after my own in the end of this Preface. 

 I have altered the method in which they are published, pur- 

 posely to bring them into less room and better order for 

 the service of those that have occasion to make use of them. 



In the same Transactions are printed some observations 

 of the greatest elongations of Jupiter's satellites from him ; 

 whereby the diameters of their orbits were determined in 

 such parts as Jupiter's is one. These I found larger than 

 Signor Cassini had determined them, in his Satellite Tables, 

 1668 : but I suspect them less than the real truth, by reason 

 that the diameter of the planet appears bigger than it is, by 

 reason of the breadth of the pupil of the eye. 



In the month of March of the following year, 1673, from 

 the observations of Jupiter's distances from the 9th of Virgo, 

 or the last of the four in the left wing, I determined the 

 greatest inclination of the orbit of Jupiter to be less than 

 the latitude of this star, by 26' 40'. Its latitude in my new 

 catalogue, is 1° 46' 10" south : whence the greatest inclina- 

 tion of his orbit will be 1° 19' 30". These observations, 

 with the process whereby it was determined, were printed 

 by Mr. Oldenburg in his Transactions, No. 94, for May 19, 

 1673. 



It was this year also, as I remember, I wrote a small 

 tract in English, concerning the true diameters of all the 

 planets, and their visible, when at their nearest distance 

 from our earth, or their greatest remove from it ; which I 

 sent to Mr. Newton in the year 1685, who has made use 

 of it in the 4th book of his Principia. 



From some observations of the eclipses of Jupiter's Satel- 

 lites made this year, their mean motions were corrected by 

 me: those of M. Cassini published in the year 1668, and 

 imparted to me by Mr. Townley, having showed themselves 

 very faulty. 



