[ 20 6 ] 
an uniform Motion about the upper Focus, for the 
Orbit of a Planet ; or that of a Motion in a Parabola 
for the perihelian Part of the Orbit of a Comet ; or 
fome other fuch) it would be impoffible to proceed 
one Step in it. But as no general Rule has ever yet 
been laid down, to aflift this Method, fo as to make 
it always operate, it is the fame in Effed as if there 
were no Method at all. And accordingly in Experi- 
ence it is found, that there is no Rule now fubfifting 
but what is absolutely ufelefs in the Elliptic Orbits of 
Comets 5 for in fuch Cafes there is no other way to 
proceed but that which was ufed by Kepler : To com- 
pute a Table for fome Part of the Orbit, and therein 
examine if the' Time to which the Place is required, 
will fall out any- where in that Part. So that, upon 
the whole, I think, it appears evident, that this Pro- 
blem (contrary to the received Opinion) has never yet 
been advanced one Step towards its true Solution : A 
Consideration which will furnifh a fufficient Plea for 
meddling with a Subjed fo frequently handled ; efpe- 
cially if what is offered fhall at the fame time appear 
(as I truft it will) to contribute towards Supplying 
the main Defed. 
Lemma L 
