An original theory or new hypothesis of the universe /

by Thomas Wright

The Increase of her Lustre, indeed, during the Absence of the Sun from us, to a less penetrating Genius than your's, may possibly afford some trifling Ground of Objection to the above Conclusions, as being drawn from the Phænomena of Day-light only; by reason in the Night, we have no Clouds in equal Circumstances to compare with her.

But this I need not tell you, is all owing to her being seen through a darker Medium, and not to any real Increase of natural Light emitted from the Sun. As a Proof of which, were it necessary, you need only, shut out the Rays of the Atmosphere, by the Help of a sufficiently long Tube; and the Moon, or any other celestial Body, will appear through it, as bright in the Day-time as in the Night.

Thus all light Bodies of inferior Lustre, whether shining by their own natural Radiences, or by a borrowed Reflection, partake of the same Advantage, when removed from the more potent Influence of a superior one; and hence it is, that the [M]Aura Ætherea shines out most manifest, when the Body of the Sun himself is hid, the Stars, and the Via Lactea most lively and numerous in the Absence of the Moon, and those Exhalations, or Meteors, vulgarly called Falling-stars, become only visible (like Glow-worms) in the Night.

[M] An Helios, or golden Light, always attending the Sun, and supposed to spread itself all round his Body in the Direction of his Equator, was very visible during the total Darkness of the Eclipse of 1715, and may be always seen about the Autumnal Equinox.

Here it may not be improper to tell you, that the Clouds are to us in effect no other than as so many Moons, whereby we have our artificial Day prolonged to us several Hours after the Sun is set, and likewise produced as much sooner before he rises; and were they to ascend by still stronger Power of Exhalation to an Elevation, all round the Atmosphere, so as to form a Sphere equal to four Times the Globe of the Earth, there would then be no such Thing as real nocturnal Darkness to any Part of the World.

The lunar Light then we may very justly conclude, proceeds originally from the Sun: And notwithstanding many more Arguments might be drawn from the Demonstration of her Phases, Eclipses, &c. to prove it, yet none of them need here be added, to what has been already said, to convince you of the Truth of it. This being granted, let us now consider what Effect this, or a like Quantity of borrowed Light, would have, when removed to a much greater Distance.

I may, I think, suppose, that you know so much of Opticks as to understand, that all visible Objects apparently decrease in Magnitude, as their Distance from the Eye increases. Consequently, that, if the Moon's Orbit was placed as far again from the Earth as it really is, her Globe, or rather Disk, would then seem to be but half as big as to us she now appears to be, and of course still farther, were she placed at ten times the Distance she is known to revolve at, her apparent Diameter would be reduced to a tenth Part only of what it now appears to be in her present Orbit, that is, one hundred Times less in visible Magnitude than her neighbouring Disk is found to be where it now is seen. And such, but something less, the two Planets Venus and Jupiter, which are frequently, in their Turns, our Morning and Evening Stars, appear to be through a common Telescope.

Now these two Planets, together with the other three, which we find moving in regular Orbits round the Sun, are all found subject to the same [N]Changes of Phænomena, in their various Aspects with the Sun; and who can doubt but that they are all of the same or like Nature? But you'll say, perhaps, how are we sure that Venus and Jupiter have no native Light of their own, since many of the ancient Philosophers, and in particular Anaximander, allowed even the Moon to have some; and besides, in Philosophy, as well as in Logick, I think you hold there is no proving a Negative, at least at such a Distance.

[N] Venus and Mercury in every Heliocentrick Revolution, perform all the Changes of our Moon in a like Gradation and Defection of Light, both horned and gibos'd.

To make you conceive the Impossibility of such a Light, and next to a Demonstration, convince you of the Unnaturalness of such a Supposition, I must put you in mind, that some time ago, when I was last in the Country with you, I think it was about the latter End of Autumn, near the Winter Solstice, as we were walking one Evening, I bid you take notice of the Moon, which was then near setting, and about two Days old. You may remember, her whole Globe appeared to us very conspicuously within a manifest Circle. You immediately told me, that that kind of Phænomenon the Country People called a Stork, or the old Moon in the new one's Arms. This I then endeavoured to explain to you, and I think made you sensible it was intirely an Effect of the Earth's, and an Appearance always to be expected at that Time of the Year. The Earth being then in the State of a Full-Moon to that Part of the lunar Orbit, and near her Perihelion, at which time, the Earth sends back a Reflection to the [O]Moon twenty-five times more potent than that of the Moon to us.