CHAP. IV.
Of Light.
Thus much for the first Thing ministring to the Terraqueous Globe, the Atmosphere and its Meteors; the next Appendage is Light.[a] Concerning which I have in my Survey of the Heavens[b] shewed what admirable Contrivances the infinitely wise Creator hath for the affording this noble, glorious and comfortable Benefit to other Globes, as well as ours; the Provision he hath made by Moons, as well as by the Sun, for the Communication of it.
And now let us briefly consider the great Necessity and Use thereof to all our Animal World. And this we shall find to be little less than the very Life and Pleasure of all those Creatures. For what Benefit would Life be of, what Pleasure, what Comfort would it be for us to live in perpetual Darkness? How could we provide ourselves with Food and Necessaries? How could we go about the least Business, correspond with one another, or be of any Use in the World, or any Creatures be the same to us, without Light, and those admirable Organs of the Body, which the great Creator hath adapted to the Perception of that great Benefit?
But now by the help of this admirable, this first-made[c], because most necessary, Creature of God, by this, I say, all the Animal World is enabled to go here and there, as their Occasions call; they can transact their Business by Day, and refresh and recruit themselves by Night, with Rest and Sleep. They can with Admiration and Pleasure, behold the glorious Works of God; they can view the Glories of the Heavens, and see the Beauties of the flowry Fields, the gay Attire of the feathered Tribe, the exquisite Garniture of many Quadrupeds, Insects, and other Creatures; they can take in the delightsome Landskips of divers Countries and Places; they can with Admiration see the great Creator’s wonderful Art and Contrivance in the Parts of Animals and Vegetables: And in a word, behold the Harmony of this lower World, and of the Globes above, and survey God’s exquisite Workmanship in every Creature.
To all which I might add the Improvements which the Sagacity of Men hath made of this noble Creature of God, by the Refractions and Reflections of Glasses. But it would be endless to enumerate all its particular Uses and Benefits to our World.
But before I leave this Point, there are two Things concerning Light, which will deserve an especial Remark; and that is, its swift and almost instantaneous Motion, and its vast Extension.
1. It is a very great Act of the Providence of God, that so great a Benefit as Light is, is not long in its Passage from Place to Place. For was the Motion thereof no swifter than the Motion of the swiftest Bodies on Earth, such as of a Bullet out of a great Gun, or even of a Sound[d] (which is the swiftest Motion we have next Light), in this Case Light would take up, in its Progress from the Sun to us above thirty two Years at the rate of the first, and above seventeen Years at the rate of the latter Motion.
The Inconveniencies of which would be, its Energy and Vigour would be greatly cooled and abated; its Rays would be less penetrant; and Darkness would with greater Difficulty and much Sluggishness, be dissipated, especially by the fainter Lights of our sublunary, luminous Bodies. But passing with such prodigious Velocity, with nearly the instantaneous Swiftness of almost Two hundred thousand English Miles in one Second of Time,[e] or (which is the same Thing) being but about seven or eight Minutes of an Hour in coming from the Sun to us, therefore with all Security and Speed, we receive the kindly Effects and Influences of that noble and useful Creature of God.
2. Another Thing of great Consideration about Light is, its vast Expansion, it’s almost incomprehensible, and inconceivable Extension, which as a late ingenious Author[f] saith, “Is as boundless and unlimited as the Universe it self, or the Expansum of all material Beings: The vastness of which is so great, that it exceeds the Comprehensions of Man’s Understanding. Insomuch that very many have asserted it absolutely infinite, and without any Limits or Bounds.”
And that this noble Creature of God is of this Extent,[g] is manifest from our seeing some of the farthest distant Objects, the heavenly Bodies, some with our naked Eye, some with the help of Optical Instruments, and others in all Probability farther and farther, with better and better Instruments: And had we Instruments of Power equivalent to the Extent of Light, the luminous Bodies of the utmost Parts of the Universe, would for the same Reason be visible too.
Now as Light is of greatest Use to impower us to see Objects at all, so the Extension thereof is no less useful to enable us to see Objects afar off. By which means we are afforded a Ken of those many glorious Works of the infinite Creator, visible in the Heavens, and can improve them to some of the noblest Sciences, and most excellent Uses of our own Globe.
FOOTNOTES:
[a] It is not worth while to enumerate the Opinions of the Aristotelians, Cartesians, and others, about the Nature of Light, Aristotle making it a Quality; Cartes a Pulsion, or Motion of the Globules of the second Element, Vid. Cartes Princip. p. 3. §. 55, &c. But with the Moderns, I take Light to consist of material Particles, propagated from the Sun, and other luminous Bodies, not instantaneously, but in time, according to the Notes following in this Chapter. But not to insist upon other Arguments for the Proof of it, our noble Founder hath proved the Materiality of Light and Heat, from actual Experiments on Silver, Copper, Tin, Lead, Spelter, Iron, Tutenage, and other Bodies, exposed (both naked and closely shut up) to the Fire: All which were constantly found to receive an Increment of Weight. I wish he could have met with a favourable Season to have tried his Experiments with the Sun-beams as he intended. Vid. Boyl Exp. to make Fire and Flame ponderable.
[b] Astro-Theol. Book 7.
[c] Gen. i. 3. And God said, Let there be Light, and there was Light.
[d] It may not be ungrateful to the Curious, to take notice of the Velocity of these two Things.
According to the Observations of Mersennus, a Bullet-shot out of a great Gun, flies 92 Fathom in a Second of Time, (Vid. Mersen. Balist.) which is equal to 589½ Feet English, and according to the Computation of Mr. Huygens, it would be 25 years in passing from the Earth to the Sun. But according to my own Observations made with one of her Majesty’s Sakers, and a very accurate Pendulum-Chronometer, a Bullet, at its first Discharge, flies 510 Yards in five half Seconds, which is a Mile in a little above 17 half Seconds. And allowing the Sun’s Distance to be, as in the next Note, a Bullet would be 32½ Years in flying with its utmost Velocity to the Sun.
As to the Velocity of Sound, see Book 4. Chap. 3. Note 28. according to which rate there mentioned, a Sound would be near 17½ Years in flying as far as the distance is from the Earth to the Sun. Confer here the Experiments of the Acad. del Ciment. p. 140, &c.
[e] Mr. Romer’s ingenious Hypothesis about the Velocity of Light, hath been established by the Royal Academy, and in the Observatory for eight Years, as our Phil. Trans. Nᵒ. 136. observe from the Journ. des Scavans; our most eminent Astronomers also in England admit it: But Dr. Hook thinks with Monsieur Cartes, the Motion of Light Instantaneous, Hook Post. Works, pag. 77. And this he endeavours to explain, pag. 130, &c.
What Mr. Romer’s Hypothesis is, may be seen in the Phil. Transact. before-cited: As also in the before commended Sir Isaac Newton’s Opticks: Light is propagated from luminous Bodies in time, and spends about seven or eight Minutes of an Hour in passing from the Sun to the Earth. This was first observed by Romer, and then by others, by means of the Eclipses of the Satellites of Jupiter. For these Eclipses, when the Earth is between the Sun and Jupiter, happen about seven or eight Minutes sooner than they ought to do by the Tables; and when the Earth is beyond the ☉, they happen about seven or eight Minutes later than they ought to do: The reason being, that the Light of the Satellites hath farther to go in the latter Case than in the former, by the Diameter of the Earth’s Orbit. Newt. Opt. L. 2. Part. 3. Prop. 11.
Now forasmuch as the Distance between the Sun and the Earth (according to the Computations in my Astro-Theology, B. 1. ch. 3. Note 2.) is 86051398 English Miles; therefore, at the rate of 7½ Minutes, or 450 Seconds in passing from the Sun, Light will be found to fly above 191225 Miles in one Second of Time.
[f] Dr. Hook Post. Works. Lect. of Light, pag. 76.
[g] For the proof of this vast Extent of Light, I shall take the Computation of the same great Man, pag. 77. If, saith he, we consider first the vast Distance between us and the Sun, which from the best and latest Observations in Astronomy, is judged to be about 10000 Diameters of the Earth, each of which It about 7925 English Miles; therefore the Sun’s distance is 7925000 Miles; and if we consider that according to the Observations, which I published to prove the Motion of the Earth, [which were Observations of the Parallax of some of the fixt Stars in the Head of Draco, made in 1699] the whole Diameter of the Orb, viz. 20000, made the Subtense but of one Minute to one of the fixt Stars, which cannot therefore be less distant than 3438 Diameters of this great Orb, and consequently 68760000 Diameters of the Earth: And if this Star be one of the nearest, and that the Stars that are of one Degree lesser in Magnitude (I mean not of the Second Magnitude, because there may be many Degrees between the first and second) be as much farther; and another sort yet smaller be three times as far; and a fourth four times as far, and so onward, possibly to some 100 Degrees of Magnitude, such as may be discovered by longer and longer Telescopes, that they may be 100 times as far; then certainly this material Expansion, a part of which we are, must be so great, that ’twill infinitely exceed our shallow Conception to imagine. Now, by what I last mentioned, it is evident that Light extends it self to the utmost imaginable Parts, and by the help of Telescopes we collect the Rays, and make them sensible to the Eye, which are emitted from some of the almost inconceivably remote Objects, &c.——Nor is it only the great Body of the Sun, or the vast Bodies of the fixt Stars, that are thus able to disperse their Light through the vast Expansum of the Universe; but the smallest Spark of a lucid Body will do the very same Thing, even the smallest Globule struck from a Steel by a Flint, &c.