VOL. LXXVI.] PHILOSOPHICAL TRANSACTIONS. 149 



posed by the Royal Academy of Sciences at Paris, to compute the disturbances of 

 the comet of 1532 and l6()l, and thence to predict its return.* 



If it should come to its perihelium on the 1st of January 1789, it might pro- 

 bably be visible, with a good achromatic telescope, in its descent to the sun, the 

 middle of September 1788, and sooner or later, according as its perihelium should 

 be sooner or later. It will approach us from the southern parts of its orbit, and 

 therefore will first appear with considerable south latitude and south declination ; 

 so that persons residing nearer the equator than we do, or in south latitude, will 

 have an opportunity of discovering it before us. It is to be wished that it may be 

 first seen by some astronomer in such a situation, and furnished with proper in- 

 struments for settling its place in the heavens, the earliest good observations be- 

 ing most valuable for determining its elliptic orbit, and proving its identity with 

 the comets of 1532 and l6dl. The Cape of Good Hope would be an excellent 

 situation for this purpose. In order to assist astronomers in looking out for this 

 comet, I have here given its heliocentric and geocentric longitudes and latitudes 

 and correspondent distances from the sun and earth, on supposition that it shall 

 come to its perihelium on Jan. 1, 1789. But if that should happen sooner or 

 later, the heliocentric longitudes and latitudes and distances from the sun will 

 stand good, if applied to days as much earlier or later, as the time of the perihe- 

 lium may happen sooner or later; and the geocentric longitudes and latitudes and 

 distances from the earth must be recomputed accordingly. The calculations are 

 made for a parabolic orbit from the elements determined by Dr. Halley from 

 Hevelius's observations in 1661, only allowing for the precession of the equinoxes. 

 The elements made use of were as follow : 



Time of perihelium January i, 17 89, at noon. 



Perihelium distance 0.44851. 



Place of ascending node 2^ 24° 1 s'. 



Inclination of orbit to the ecliptic 32° 36'. 



Perihelium forwarder in orbit than the ascending node 33° 28'. Its motion 

 is direct. 



• Since this was written, I received the unwelcome news, in a letter from M. Mechain, of the 

 Royal Acad, of Sciences at Paris, that the Academy has not received satisfactory answers concerning 

 the disturbances of the comet between 1532 and I66I, and 1661 and the approaching return, and 

 that the prize is referred to be adjudged of at Easter 1788, and that it will be 6000 livres. N. M. 

 — Orig. 



