Time takes its first Denomination from the diurnal Rotation of the Earth upon its Axis, which we call a natural Day, and this for obvious Reasons we subdivide in twenty-four Parts or Hours. This diurnal Motion having been successively repeated, and the Day renewed three hundred and sixty-five Times, we find that all the vegetable World has gone through all its Variegations, and Nature has again put on the same Face, adapted to the Season; during which Time, and indeed which occasions this general Change and Repetition, the Earth is found to make one intire Revolution round the Sun. This Space, or Period of Time, we call a solar, or rather a natural Year; and from our Sensibility of this, and its constituent Parts, both horary and diurnal, we form our general Judgment of Duration.
Saturn, the most remote, and most regular Planet in our System, as has been said before, performs one Revolution round the Sun in about twenty-nine of the above solar Years: The great Comet of 1680 makes but one periodical Return in five hundred and seventy-five of those Years, and the general Motion of the Stars, arising from the Procession of the Equinoxes, altogether continually changing their Aspect, or Position, at the Rate of 50″ per Year round the ecliptic Poles, compleats but one Revolution in 25920 Years; in which Time the whole sidereal Frame of Heaven has changed, and every Star returned to the same Point of the solar Sphere it set out from. This is by many called the great Saturnian Year: Concerning which, Mr. Addison has thus translated an eminent Author.
When round the great Saturnian Year has turn'd,
In their old Ranks the wandering Stars shall stand,
As when first marshall'd by the Almighty's Hand.
Now, if this sidereal Revolution, arising from a secondary Cause, require this Number of Years to perfect one Rotation, what must their primitive Orbits take to circumscribe the Vortex Magnus.
It has been observed, that the biggest Star to us scarce moves a Minute in an hundred Years, and the most remote as insensibly for Ages, from whence and what has been already said of the imagined Distance of the general Center, we may frame this probable and well-grounded Guess, that the mean Revolution of a Star near the Middle of the Vortex Magnus, cannot be made in less than a Million of Years, and though to us imperceptible, our Sun in his own orbicular Direction, may be moving many Miles per Day. Besides, if local Motion can be proved amongst the Stars, what less than an Eternity can again restore them to their original Order and primitive State. Such vast Room in Nature, as Milton finely expresses it, cannot be without its Use; and nothing but absolute Demonstration is wanting (which from their Nature and Distance cannot be expected) to confirm the grand Design, so suited to the Deity's infinite Capacity, and of eternal Benefit to all his Creatures, especially Beings of a rational Sense, and in particular Mankind.
Of these habitable Worlds, such as the Earth, all which we may suppose to be also of a terrestrial or terraqueous Nature, and filled with Beings of the human Species, subject to Mortality, it may not be amiss in this Place to compute how many may be conceived within our finite View every clear Star-light Night. It has already been made appear, that there cannot possibly be less than 10,000,000 Suns, or Stars, within the Radius of the visible Creation; and admitting them all to have each but an equal Number of primary Planets moving round them, it follows that there must be within the whole celestial Area 60,000,000 planetary Worlds like ours. And if to these we add those of the secondary Class, such as the Moon, which we may naturally suppose to attend particular primary ones, and every System more or less of them as well as here; such Satellites may amount in the Whole perhaps to 100,000,000, or more, in all together then we may safely reckon 170,000,000, and yet be much within Compass, exclusive of the Comets which I judge to be by far the most numerous Part of the Creation.
In this great Celestial Creation, the Catastrophy of a World, such as ours, or even the total Dissolution of a System of Worlds, may possibly be no more to the great Author of Nature, than the most common Accident in Life with us, and in all Probability such final and general Doom-Days may be as frequent there, as even Birth-Days, or Mortality with us upon the Earth.
This Idea has something so chearful in it, that I own I can never look upon the Stars without wondering why the whole World does not become Astronomers; and that Men endowed with Sense and Reason, should neglect a Science they are naturally so much interested in, and so capable of inlarging the Understanding, as next to a Demonstration, must convince them of their Immortality, and reconcile them to all those little Difficulties incident to human Nature, without the least Anxiety.