2£)£) ON* THE PLANET CERES. 



Piazzi's firft obfervation, and alfo for the 26th of Jan. 1802, 

 as given by the laft obfervation of Von Zach in the prefent 

 extract, and project the orbits of the earth and Ceres accord- 

 ing to the eccentricity, mean diftance and place of the aphe- 

 lion of Gaufs, as given in the extract from the Moniteur in 

 the different journals, we flia.ll have the figure reprefented 

 in Plate XIII. Fig. 1, which is thus conftructed, viz. 

 Conftruftion of Suppofing the point S to be the fun, defcribe, with any 

 the orbits of the rad j u the eirde mar k e( j T ^ n , &c. for the ecliptic, 

 earth and Ceres, ... ' * , i • 



with the geocen- and conceive it to be at an infinite diftance; draw an occult line 

 trie and helio- f rom $ to © 9|°, the earth's aphelion, and another to zz 26| °, 

 the latter Sec the aphelion of Ceres ; take 10 from- a fcale of equal parts, 

 and defcribe with that radius the innermoft circle A P from 

 a point -g s of the radius from S towards A in the occult line, 

 and another circle with a radius of 27,6 of thofe equal parts 

 -from the point C —^ of the faid radius from S in the fecond 

 occult line, and thefe circles, which are eccentric with re- 

 fpecl to the fun at S, will very nearly reprefent the required 

 orbits of the earth and Geres, in both which A reprefents the 

 aphelion, and P the perihelion points. In the next place find 

 the two points in the earth's orbit, w r hich are diametrically 

 oppofite the fun's place for Jan. 1, 1801, at 9 h P. M. and 

 Jan. 27, 1802, at 4 h A. M. which will be s 11° 1' 33" and 

 Si 6° 35' refpectively, and mark them as in the figure with 

 their dates ; after this mark the geofcentric right afceniions of 

 Ceres (denoted by the letter C with a crofs beneath) for 

 Jan. 1, 1801, and G at 8 21° 47' 48'', according to Piazzi, 

 and for Jan. 26, 1802, at G at ^CC 8° 24', according to Von 

 Zach, and draw the two dotted lines from S to each ; then if 

 dotted lines be drawn parallel to thefe two lines from the earth 

 (0) in Jan. 1801 and 1802 refpectively, until they touch the 

 orbit of the planet Ceres, thefe laft lines will mark the geo- 

 centric apparent places of this planet in its orbit, of which the 

 dotted lines from S to the ecliptic denote the meafure ; and, 

 laftly, if lines be drawn from S through the geocentric places 

 to the ecliptic to H and H, they will indicate the heliocentric 

 longitudes, and the arcs contained between the heliocentric 

 and geocentric meafures will be on each day the meafure of 

 The method of what is called the parallax of the orb. — This method of con- 

 converting geo- verting geocentric into heliocentric places by projection is 



centric portion u i c % . r r T i . . , 



ima heliocentric ca P a °le oi great accuracy, and is, io tar as I know, original. 



Thr 



