ON THE 1>LANET CERES. 285 



until the elements of its orbit (hall be accurately affigned, it 

 may be acceptable to many readers of your Journal to have a 

 popular detailed account laid before them of the manner of 

 applying obfervations to determine the whole period and form 

 t)f the orbit, in order that they may comprehend, and confe- 

 quently feel an intereft in, the perufal of the different notices 

 which will, mod probably, be publiflied from time to time in 

 different countries. 



When a heavenly body is firft fufpeded to be a planet, the How a planet is 



r r ■ • r • i r > r a j x difcoveted— -by 



lulpicion ariles either from its apparent atpect compared to a its a f pe a 



•ftar when viewed in a telefcope, as was the cafe with Geo. through the te- 



Sidus, or otherwife on account of an obferved change of re- gj^l 



lative fituation, as was the cafe with the new planet Ceres 



when compared with forae fmall ftars in its neighbourhood z 



the firft thing to be done after the fuppofed difcovery of a new 



planet is, to afcertain its right afcenfion and declination, and 



from thence its geocentric longitude and latitude ; the means 



ufed for doing which need not be defcribed here. 



A feries of obfervations, and correlponding calculations, Subfequent ob- 



are ufually continued at fucceffive intervals, untii the newly TL Va /- tion b s f 



difcovered body has advanced or receded through inch a por- tions being made 



tion of the ecliptic as to afford data for eftimating its daily/""" the earth or 

 , , , , r i i -r r ' geocentric, mult 



velocity when compared to that or the earth : now, it a lenes be converted into 

 of obfervations could be made by an obferver in the fun, the heliocentric re- 

 arc paffed through by the planet would bear the fame propor- wou ui a p pea r 

 tion to the interval of time elapfed between the firft and laftfrw the fun* 

 obfervations, that a circle does to the whole period, provided 

 ♦the motions were equahle ; and, if the motions were unequable, 

 the obferved progreis at equal intervals would (hew whether 

 the inequalities were increments or decrements, and confe- 

 quently whether the planet was approaching the perihelion or 

 aphelion point. But the obferved places are geocentric, and 

 muft therefore be converted into heliocentric, to gain thofe 

 obfervations which an obferver placed in the fun would make ; 

 for which purpofe the proportion to be ufed will be, by a Manner of doing 

 Jimple cafe in plane trigonometry, as the diftancc of the planet thls * 

 (to be at firft affumed) from the fun : Mr to the fine of its obferved 

 elongation, or angular diftance from the fun (or its fupplement) 

 i :fo is the earth's diftance from the fun, taken from the tables, 

 : to the fine of an angle which is the difference between the 

 heliocentric and geocentric places, and which is called the 

 (parallax of the ork 



The 



