° 
THE 
MONTHLY MAGAZINE, 
No. 92.] 
OCTOBER 1, 1802. [No. 3, of Vou. 14. 
ORIGINAL COMMUNICATIONS. 
To the Editor of the Monthly Magazine. 
SIR, 
With to difcufs with the refpect due to 
aL a name to which Asrronomy is 
much indebted, the propriety of introdu- 
cing a mew order of bodies into the vo- 
cabulary of that fcience, under the appel- 
lation of Afferoids, and the principle on 
which the two ceéleftial Bodies dilcovered 
by Profeffor Piazzi and Dr. Olbers are 
propofed to be thus charatterifed. « 
If the diftinf&tion be not plainly zecefary 
and founded on facts, I apprehend it moit 
. clearly ought not to be admitted. 
Now, to try whether it be neceffary or 
not, we have to enquire whether thefe two 
bodies have no proper place aflignable to 
them in aftronomical defcription under 
the forms already in ule. 
A Planet, 1 think, is underftood to bea 
body revolving round a Sun as its centre 
iz an ellipfis not very greatly deviating 
from a circle; and accordingly capable 
of being feen, when its orbit has been 
once afcertained, in fome part of ‘every 
revolution, either by the eye or witha 
telefcope, and ufually in the whole of it. 
A Comet, IT apprehend, is a body re- 
volving in an ellipfis, very greatly devia- 
ting from a circle, and if returning (which 
both analogy and obfervation appear to 
indicate) fo liable to perturbation, and fo 
long for the molt part in its period, and 
having generally fo fhort a part of its or- 
bit within reach of obfervation, and paf- 
fing that part of it with fuch velocity, and 
fo obliquely, for the moft part, tothe paths 
of the ordinary planets, that it may eafily 
revolve without being obferved at all. 
The other circumnftance of its being ac- 
companied with a diffufed light or coma, 
though it originally gave the name, is not 
univerfal of comets. 
May it not be inferred therefore, that a 
body revolving round the fun, if with 
great eccentricity and obliquity, fo as to 
cut the orbits of the other planets or fome 
of them, may be accounted a comet ; and 
if revolving with moderate cccentri- 
city and obliquity, fo as not to cut the 
orbit of any planet, a plamet—A differ- 
ence derived from its lying out of the /- 
mits of the Zodiac feems not fufficient: 
MonTu_y Maa, N®., 92. 
the limits having been affigned by the 
early Aftronomers, with mere. reference 
to the obfervation of eclipfes of the Suz 
and IMéooz; whence the Zodiac is alfo 
termed the Ecliptic. ° 
A difference of maguitude can hardly 
exciude a celeftial body from the order of 
planets: much lefs can it place it as an 
Afterstd, if on account of its fmallnefs ir 
is.difputed whether to call it a planet. 
The difference of the magnitude of the 
planets is great and various: but the 
greateit of them is comparatively as no- 
thing to a fixed Star. Indeed a large pla- 
net between Mars and Fupiter was oreatly 
improbable, as it would much have dif- 
turbed Mars. Names of /militude, as 
Linn#us has obferved, are too vague to 
be well fuited to {cience. Even if in this 
inftlance a new name were required, this 
would be no flight objeGtion to the choice 
of the name, and befide, how flight the fi- 
militude ? It confifts merely in refemblance 
to a telefcopic ftar. But fome comets have 
had the fame refemblance: fome of the 
fatellites of Jupiter and Saturn have this 
refemblance: and the Herfchelian Planet 
itfelf. The points of diffimilitude between 
a fmall body fhining by refleGted light and 
revolving round a fun, and a fixed ftar or 
fun, are incomparably greater than the 
fingle point of refemblance; faint and 
imperfect as it is in that folitary particular 
itfelf. 
The Piazzi feems to have every claim 
to the title of a planet. 
The {mall revolving body difcovered 
by Dr. Olders feems to anfwer better to 
the idea of a comet. 
1. By the very great eccentricity and 
obliquity of its orbit. 
2. By its interfecting the orbit of the 
Piazxi planet. 
3. By its very fimall diftance, if: an ops 
dinary planet of the fyftem, from the 
Piazzi: a circumftance incompatible 
with the beautiful harmony of diftances, 
fuggelted by Bode, and with which the 
Piazzi fo well agrees. The maxim that 
names in fcience are not lightly to be 
multiplied, Nomina non funt temere multi- 
plicanda, ‘eems molt torcilly toapply here. 
We should fee very clear and determi- 
Cec nate 
