Shares in the like Motion, fo we may very reasonably imagine that it is no lefs ufeful and beneficial to them than it is to us, and that the Inconveniences of the want of it would be as great.

CHA P. IV.

Of the Annual or Periodical Motion of the Primary Planets.

B

ESIDES the Motion treated of in the preceding Chapter, there is another, which is as clear a Manifestation of the great CREATOR as that, namely the Periodical or Annual, which is vifible in fome of the great Globes, and probable in many others. Among the Fixt Stars it is highly probable fome

thing

thing of this Nature is: as appears from thofe New Stars which I have before taken notice of, which, as I have faid, fometimes become vifible to us, in one Part of their Orbits, and again difappear in other Parts of them. But these Systems being out of the Reach of our best Glaffes, I fhall pafs them by, efpecially because in our own Solar Syftem, we have abundantly enough to entertain us in this Demonftration of GOD.

For it is very vifible, without the Help of the Telescope, that every Planet of the Solar System hath this Periodick Motion I am fpeaking of. For it is manifeft that either the Sun and the Planets move about the

Earth, the one in the space of a year, and the reft in other times; or that the Earth and the other Planets move about the Sun in fuch times. But let us (as I have all along done) fuppofe

the latter, that the Sun is fixt in the Center, without any other but its Diurnal Rotation in 25 Days: in this cafe we shall have the feveral Primary Planets revolving round the Sun in an excellent and due Order, by the exactest Rules of fuch a noble Structure, fuch an admirable Oeconomy, and that is in Times (as I faid) in Square proportion to the Cubes of their Diftances. So that we see Mercury to perform its Period in near 88 Days: Venus (the next in order to the Sun) its Period in fomewhat above 224 Days: then the Earth, with its Companion the Moon, in 365 Days: then Mars in about 687 Days: next him Jupiter in about 4333 Days: and laftly, Saturn in fomewhat above 10759 Days.

4

To this fo ftrict an Order of the Periods of those Planets, we may add the confideration of the different Paths of their Periodical and Diur

nal

very

nal Motions: that they lie not in a different Plane, as quite acrofs, or the like; nor exactly in the fame Plane, but a little croffing one another; the Diurnal Course lying in, or parallel to the Equator; but the other in the broad path of the Zodiack at an inclination of 23 Degrees.

I

And a glorious Contrivance this is for the Good of our Globe, and doubtless no lefs for all the rest that fympathize in the like Motion.

For

was the Earth's Periodick Motion to be always in the fame Plane with that of the Diurnal, we might indeed be fometimes nearer to, and fometimes farther from the Sun; but at the fame time mifs of those kindly increases of Day and Night, together with fuch ufeful directions of the Sun-beams, which the advances of the Earth to one or other of the

Poles

Poles caufe (a): which two things are the real Causes of our Seasons of Summer

(a) There are two Causes of the great difference between the Winter and Summer, Heat and Cold. One is the fhorter or longer continuance of the Sun above the Horizon in Summer long, which increases the Heat, as much as it lengthens the Day: in Winter fhort, which diminishes the Heat, as it fhortens the Day; and augments the Cold, as it lengthens the Night. The other Cause is the Oblique or Perpendicular Direction of the Sun's Rays, the Oblique being weaker than the Perpendicular; as is evident from Galileo's Experiment, in his Syftema Mundi, Dial. 1. by holding a Paper turned up at right Angles, or a Book half open; over against an illuminated white Wall; where it may be observed that the Side oppofite to the Wall, which the Rays ftrike perpendicularly, is far more light and white than the other Side, on which the Rays fall obliquely. The fame it is in the Incidence of the Sun's Rays on any Plane, namely, the Rays are so much stronger, and the Plane the more warmed and enlightened, as the Rays are more or lefs Perpendicular; and that on two Accounts; 1. Because the Perpendicular Rays ftrike with greater force than the Oblique. As in Fig. 4. the Rays RR ftrike the Plane AP more forcibly than the Plane O B. The Action or Force of which Percuffion is (like that of all other Impulses) as the Sine of the Angle of Inci

dence