whereas otherwife, upon the Setting of the Sun in all Places, a bright Day would be immediately changed into a Pitch-dark Night? And it may be easily perceived, that it is fo ordered on purpofe to be useful to Men, the Organs of whose Sight would be very much prejudiced, if the Tranfition from much Light to much Darkness were made all at once: But they that would be more fully informed in this Matter, need only look back to what we have faid in the 17th Contemplation about it.

That which may be farther obferved here, is, with how much Reason God, to convince Job of the Narrowness of his Understanding, has taken a Proof thereof from this Refraction of Light in the following Words; Chap. xxxviii. v. 12. Haft thou commanded the Morning fince thy Days? And cauJed the Day-Spring to know his Place? Which laft Words are tranflated by Pool and others. Do you know perfectly the Place of Twilight?

To make this more intelligible to those that are unexperienced in Mathematicks, we have fhewn above, in Tab. XIV. Fig. 3. that the Sun A being under the Horizon E Y, and cafting its Rays A H upon the Air at H, the faid Rays do not proceed directly, and in a ftrait Line to D; but by being inflected, and making an Angle AHF, they are turned afide to F, and refracted or broken at H, and thereby produce Day-break or Twilight to those that live at F. Now it is known to every one by numberlefs Experiments, that according to the greater or leffer Thickness or Density of the Air, which varies in different Places, and in the fame Place too, at different times, for many Reafons, the Refraction does likewife differ: And therefore, that the Twilight, with respect to the extreameft Parts where it is feen upon the Earth, or in the Air, cannot be determined by any Bo

dy;

dy; fo that the faid Question feems to carry this Meaning along with it. Did you ever truly underftand the different Thickness of the Air, both in your own and other Climates of the World, or the greater or leffer Refraction proceeding from thence, and confequently the Variations of the Morning and Evening Twilights, which are the Refult thereof; or have you any Command or Direction over it? To which Propofition no Mortal will ever be able to return any other Answer, than that this has always been myfterious and impracticable to him; to convince holy Job whereof, was the Defign of the Almighty.

Befides what has been juft now faid, there may be still added these Reasons, why 'tis impoffible for Men to know exactly the Place of the Twilight: First, Because it seems neceffary to be fuppofed, that the Sun is encompaffed with a kind of an Atmosphere, or Circle of Vapours (as the Earth is furrounded with Air) which upon the Account of the Sun's Nearnefs, does always fhine, and is enlighten'd with the Fire thereof. Secondly, That the Sun fhining upon the Particles and Vapours floating in the Air, the Rays are fent back from fome of 'em, as it were from a Looking-Glafs by Reflexion, to the People who begin already to enter into Night; both which contribute very much to the Production of the Morning and Evening Twilight: See concerning this, Gregory's Aftronomy, p. 127. where that great Mathematician (as if he intended to corroborate our Interpretation) uses the following Expreffion; For thefe Reasons the Bounds or Place of the Morning and Evening Twilights are not fo certain: Befides which, he alledges feveral other Caufes of this Uncertainty.

SECT. XVI.

SECT. XVI. The Weakness of our Conceptions.

Now forafmuch as all the great Services which the Sun renders to Men, Beafts and Plants are not to be number'd; forafmuch as we fee them daily renewed; forafmuch as if we had been blind before, or remain'd always in Darkness, we fhould be ftruck with Wonder, and, as it were, transported at the Glory of the Sun's firft Appearance: I have often stood amazed, how it was poffible, that not only the Atheists (who act herein according to their Principles) but likewife others that acknowledge a God, and that pretend to worship him upon other Occafions, are fo little affected with all the Advantages that accrue to them from the Sun: For inftance, how few are truly thankful for this great Benefit, that God caufes the Sun to rife in the Morning and enlighten the World, and to fet in the Evening and produce the Night, by the Shadow of the Earth, in order to give Reft to all Creatures that have been tired by the Labour of the Day; and fo in other Matters.

But particularly even those who are now entirely convinced of the Magnitude of the Sun, and its great Distance from the Earth, by the Mathematical Demonftrations of the Aftronomers, as well as by fo many Places of the Holy Scriptures; fuch as Pf. lxxiv. v. 16. Thou haft prepared the Light and the Sun. And Pf. cxxxvi. v. 7. To him that made great Lights; and many others, have feen that the Spirit of God himself has appointed this great and glorious Body for a certain Proof of the infinite Power of the Maker and Ruler thereof; and yet they hardly feem to have formed a right Notion of it. Befides Cuftom, the Weakness of our Imaginations feems to be the

principal Cause thereof, which is unable, as well by reafon of the Smallness of many Creatures that we are forced to view with Microscopes, as becaule of the Greatness of these heavenly Bodies, to reprefent them properly to us: And tho' no Body that understands Demonftration can doubt thereof, yet every one will find how defective his Imagination is in forming juft Ideas of their real Greatness or Smallness: Of this we have no Occafion to produce any Proofs; let every Man only examine himself, and fee whether he does not discover within him, what many of the greatest Mathematicians are obliged, with Shame to confefs, that they themselves experience concerning this Matter: See what Mr. Huygens fays about it in his Cofmotheoros, p. 124, and 125, who, to obviate this Weakness of the Humane Imagination, endeavours to make use of another Means, to impress more ftrongly upon our Minds the Greatnefs of the Works of our adorable Creator, and of the Distance of the Sun from the Earth; fhewing, that if we fuppofe with him, that the faid Distance amounts to 12000 Diameters of the Earth (which yet is much lefs than what the Modern and moft Accurate Aftronomers do with good Reason maintain) a Bullet fhot out of a great Cannon, and moving in an equal Degree of Velocity, will be 25, or at leaft 24 Years in paffing from the Earth to the Sun.

SECT. XVII. How much Time is required for a Cannon Bullet to pass from the Earth to the Sun.

Now that what has been advanced by Mr. Huy-. gens does not exceed the Truth, will appear:

I. Because, according to the most exact Menfuration by the French Mathematicians, a Degree of a Great Circle upon the Globe of the Earth

amounts

amounts to 57060 Toifes or Fathoms of fix Foot; from whence it follows, that the Diameter thereof amounts to 6,538594 of the like Fathoms, according to the faid Mr. Huygens and Whifton in his Pralect. Aftron. p. 13.

II. This being multiplied by 12000, the Diftance of the Sun from the Earth, amounts to 78,463.128,000 of French Fathoms.

III. Now by the Experiments of Mersennus, a Cannon-Bullet advances in a Pulfe, or the Second of a Minute, about a hundred of the aforefaid Fathoms, it therefore requires 784.631,280 Seconds to pass with the like Swiftnefs from the Earth to the Sun.

IV. This Number is fomewhat fmaller than 788.940,000 which are the Sum of the Seconds in Twenty-five Years, if one allows to each of 'em 365 Days and 6 Hours, as may appear by the Calculations of the faid Mr. Huygens.

SECT. XVIII. How much Time is required for a Ship, or any Living Creature that can run Fifty Miles in a Day and a Night, to pass from the Earth to the Sun, and Convictions from thence.

Now if the Swiftnefs of a Cannon-Bullet fhould too much dazzle any ones Imagination; let him fuppofe a nimble Animal, fuch as a Horse, a Deer, a Bird, as also a Ship, either of which, if they can advance Fifty Miles every Twenty-four Hours, will require at least 1000 Years, either to run, fly, or fail, fuch a Space, as is between the Sun and the Earth; which may be eafily computed, if one again fupposes:

I. That the Sun is diftant from the Earth 12000 Diameters thereof.

II. That a Degree, according to a Pilot's Calculation, being fifteen Dutch Leagues, the Circum

ference