Summer and Winter, Spring and Autumn, and not our being nearer unto,

dence. So the Force of the Rays RR upon the Oblique Plane O B, is as the Sine only of ROB, whereas their Force upon AP is as the whole Sine of 90 Degrees, or Angle ROP. 2. Another Reafon is, That a greater Number, or Quantity of Rays, fall within the Compafs or Area of any Plane, in a perpendicular, than oblique Direction. This will be manifeft from the bare infpection of Fig. 4. where it may be observed that all the Rays between R R and Op fall on the Plane AP; but only about one half of them would fall upon an oblique Plane of the fame Length, if it was Ob: Or (which is the fame thing) near as many Rays would fall off Ob, turned up to Ob, as fall upon it. Also it may be obferved farther, that as the Line OB is longer than Op fo are the Spaces between the Rays larger in OB than Op; and confequently fewer Rays fall on O B for its Length, than on Op for its Length, or the Rays are denfer, or more compact in Op than O B. And when they are fo, they are so much the ftronger, as is evident from the collecting and condenfing the Sun's Rays by a Burning-glass.

What the particular Power of the Sun's Rays is in all Directions, Quantities, and Impulfes, falls under Mathematical Calculation; but I need not trouble the Reader with it, but fhall refer to the ingenious Dr. Wolfius (Mathematical Pro

feffor

For

to, or farther from the Sun. thofe Benefits (we at least that inhabit towards the Northern Pole) have at the contrary Season, when we have most need of them, viz. the Sun's Proximity, in Winter; its greater Distance from us in Summer; as is manifeft from the Increment of its apparent Diameter in Winter to 32', 47", and the Decrement thereof in Summer to 31', 40′′. (b).

And

feffor of Hall) his Elementa Aerometria. And as for the proportional Degree of the Sun's Heat in all Latitudes, and its Altitudes, our most acute Savilian Profeffor, Dr. Halley, hath given us a neat and clear Method for computing it in Philof. Tranf. No. 203.

(b) Monfieur de la Hire in his Tabul. Aftron. makes the Sun's Semidiameters to be Dec. 30. 16′ 22′′ and Jun. 30. 15′ 49′′. But Mr. Flamfteed in his Lunar Tables added to Mr. Horrox's Pofthumous Works, makes the greatest to be 16' 23, the least 15' 50" and the French Academift 16' 23" and 15' 50". V. Recueil d' Obferv. Les Elemens d' Aftron. p. 22.

Befides the Alteration of the Sun's apparent Diameter, its fwifter Motion in Winter about

the

And now for a Conclufion of this Chapter concerning the Periodick Motions of the Primary Planets, we may take up the Argument of Hugo de S.Victore (c), Who commandeth the Sun to defcend through the Winter Signs? And who again caufeth him to afcend through the Summer Signs? Who leads him from Eaft to Weft? And who again brings him back from the Weft to Eaft? All these things are very wonderful, but to God alone poffible.

the Solstice by about a 15th part, is an Argument of its being then nearer the Earth. From whence it comes to pass that from the Vernal to the Autumnal Equinox, there are about 8 Days more, than from the Autumnal to the Vernal.

(c) Quis folem per hyberna defcendere figna præcipit? Quis rurfum per æftiva figna afcendere facit? Quis eum ab Oriente in Occidentem ducit? Quis iterum ab Occidente in Orientem revebit? Hæc cuncta funt mirabilia, fed foli Deo poffibilia. Didafcal. L. 7. c. 8.

С НА Р.

CHAP. V.

Of the Periodical Motion of the Secondary Planets.

AVING confidered the Peri

Hods of the Primary Planets,

let us next caft our Eye upon those of their Secondaries. And among these we shall find the fame compleat Order and Harmony as among the laft. Thus Saturn's five Moons, and Jupiter's four, and our own about the Earth, have each of them their determinate Times, fome longer, fome fhorter Intervals of Time, in the fame due Proportion, as I spake of among the Primaries.

Befides which, there is another Thing very confiderable in this periodical Motion of thofe Secondary Planets,

H

Planets, and that is, that it is mixt with a kind of cochleous Direction towards one or other Pole of the primary Planet; by which means every Satellite, by gentle Degrees, makes its Vifits towards each 'Pole of its Primary. This is well known among the Circumjovials for inftance, that they all have a flow and gradual fcrew-like progress, firft towards one, then back again towards the other Pole of Jupiter: and that each Satellite hath its Declination greater and greater, according as it is farther or farther from Jupiter's Body. Accordingly the Declination of each Circumjovial, affigned by the diligent and fagacious Caffini (d), after twelve Years Obfervations, are thefe, The greateft Declination of the

.

(d) Les Hypoth. & Les Tables des Satel. de Jupiter, S. 4 in the French Academift's large Collection.

First,