44

A S T R O N O M Y.

the shortest Diameter: And in on e ^these Focus’s, viz. S, the Sun is P^jtabout which the Planet moves in the 0 {

ABPD (CXL).

PI. LVI.F; g- 3*

(CXL) i. We have hitherto considered the P «c'mena of the Heavenly Bodies without regard to tcurate Form of their Orbits, which is not circul ^ 1 ^elliptical ; yet that it is very little so, even in ti>e^ hseccentric Orbit, as that of Mercury , will app e pis'comparing their Eccentricities with their m eSsl pi !'tances from the Sun. Thus suppose the m eaI1tance of the Earth from the Sun be divided in t0equal Parts, then in those Parts we have,

In Mercury,

, CS :

DS ::

: So :

387 :

: 1 :

■ , J

Venus,

CS :

DS ::

: 5 :

723 :

: I :

Earth,

CS :

DS ::

: 17 :

1000 ::

: 1 :

59 n f?

Mars,

CS

: DS :

: 141 :

: 1524 :

: 1

Jupiter,

CS

: DS :

: 250 :

: 5201 :

: 1

. 'I'Jt

■t '?* 4 >

Saturn,

CS

: DS :

: 547

: 9538 :

: 1

: IV*

:* c Ot

2. It is round by Experience that the Ortu^Planets are quiescent, or that the Line of the ^ pAP always keeps one and the fame Positionspect to the Fixed Stars : And the Apheliunt, ° { e feVA, possesses different Points in the Ecliptic in thral Orbits as follows. ' y

o

In Mercury , t 12 44 00

Venus, ~ 4 19 54

Earth, y 8 1 10

o ' " " j

In Mars, M 0 3 q

Jupiter,* 9 1 r

Saturn, t 2 7 ^ji

3, That the Earth’s Orbit is elliptical is vveHfrom common Experience ; for were the Orbitsthe Sun’s apparent Diameter would always be th ^ wbut we find it is not, for if it be measured rvltN ^crometer in Winter-time, it will be found com* 0 ^larger than in the ‘Summer, and it will be s£ ea ^ d 1 ?all when the Sun is in the 8® of Vf, (which m ev ’