the Preneb National Inflitute. 423 
effects of parallax, aberration and nutation, in order to ob- 
tain the true pofitions, and that there may be no need to 
employ, in the calculation of the geocentric places, but the 
longitudes counted from the mean equinox. 
2. To employ in the calculus the true place of the fun; 
that is to fay, augmented 20 feconds for aberration, and 
counted from the mean equinox. 
3. To give, for each obfervation, the difference of the 
obferved place of the comet, and that deduced from calcula- 
tion; and to join to thefe differences the correétions to be 
made in the heliocentric longitudes and latitudes, in order 
to make the error of the geocentric places vanifh. | 
4. To give the error which muft be produced on the 
geocentric place by an error of 10 feconds in the calculated 
longitude of the fun; and to determine alfo the effect of a 
fmall error in the radius vector of the earth. 
5. Laftly, though the nebulofity which furrounds comets 
generally prevents their phafes from being well diftinguithed, 
it will not be ufelefs to examine whether thefe phafes could 
have had any fenfible influence on the obferved places; 
and, in that cafe, they muft be taken into the account, if 
poffible. 
By paying attention to all. thefe points, which, for the 
moft part, have been hitherto neglected, it may be at length 
poffible to difcover whether the movements of that comet 
may not really be reprefented in a non-re-entering orbit, ~ 
or whether the irregularities obferved in its courfe may not 
have been owing, 
earth’s orbit, which are not perhaps fufficiently well de- 
termined to give with precifion- the geocentric places of a 
planet which approached fo near the earth. 
The prize is a kilogramme of gold. Papers on this fub- 
je& will not be received beyond the 15th of Meffidor, 
An. VIII. The'Inftitute will announce the piece which 
has gained the prize in its public fitting of Nivole 15, 
. An, TX, 
in a great meafure, to the elements of the 
Ee PRO« 
