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without controversy; nor were the doctrines now prevalent believed in former times. And even now the question whether Mercury or Venus be the higher, is still pending. Now distances are discovered either from parallaxes, or eclipses, or calculations of motions, or differences in apparent magnitude. And other aids are to be provided for the determination of this, which may be devised by human industry. The thicknesses or depths of the spheres also have relation to distances.





SEEING then that there are such difficulties on all sides, we must be content if something be asserted that is not harsh. I will myself therefore construct a Theory of the Universe, according to the measure of the history as yet known to us; keeping my judgment however in all points free, for the time when history, and by means of history my inductive philosophy, shall have been further advanced. Wherein I will first propound some things respecting the matter of the heavenly bodies, whereby their motion and construction may be better understood; and then I will bring forward my thoughts and views concerning the motion itself, which is now the principal question. It seems then that nature has in the distribution of matter separated fine bodies from gross; and assigned the globe of the earth to the gross, and the whole space from the surface of the earth and waters to the very extremities of the heaven, to the fine or pneumatic, as the two primary classes of things, in proportions not equal indeed, but suitable. And this is the natural and proper collocation of things, nor is it confounded either by water hanging in the clouds or wind pent within the earth. Now this distinction of fine or pneumatic and gross or tangible, is quite primordial, and the one which is most employed in the system of the universe. And it is derived from that condition of things which is of all the simplest, namely the quantity and paucity of matter in proportion to bulk. The pneumatic bodies which are found here with us (I speak of such as exist simple and perfect, not compound and imperfectly mixed), are those two, Air and Flame. And these are to be regarded as bodies

altogether heterogeneous; not as is commonly imagined, that flame is only air on fire. To these correspond, in the upper world, the ethereal and the starry nature; as in the lower, water and oil; and lower still, mercury and sulphur; and generally, crude bodies, and fat bodies or in other words, bodies which abhor and bodies which conceive flame (salts being of a compound nature, consisting at once of crude and inflammable parts). Now for these two great families of things, the Airy and the Flamy; we have to inquire upon what conditions they have taken possession of by far the greatest part of the universe, and what office they have in the system. In the air next the earth, flame only lives for a moment, and at once perishes. But when the air begins to be cleared of the exhalations of the earth and well rarefied, the nature of flame makes divers trials and experiments to attain consistency therein, and sometimes acquires a certain duration, not by succession as with us, but in identity; as happens for a time in some of the lower comets, which are of a kind of middle nature between successive and consistent flame; it does not however become fixed or constant, till we come to the body of the Moon. There flame ceases to be extinguishable, and in some way or other supports itself; but yet such flame is weak and without vigour, having little radiation, and being neither vivid in its own nature, nor much excited by the contrary nature. Neither is it pure and entire, but spotted and crossed by the substance of ether (such as it exists there), which mixes with it. Even in the region of Mercury flame is not very happily placed, seeing that by uniting together it makes but a little planet; and that with a great perturbation, variety, and fluctuation of motions, like ignis fatuus, labouring and struggling, and not bearing to be separated from the protection of the sun except for a little distance. When we come to the region of Venus, the flamy nature begins to grow stronger and brighter, and to collect itself into a globe of considerable size; yet one which itself also waits on the sun and cannot bear to be far away from him. In the region of the Sun, flame is as it were on its throne, midway between the flames of the planets, stronger likewise and more vibrating than the flames of the fixed stars, by reason of the greater reaction, and exceeding intensity of union. In the region of Mars flame appears even robust; acknowledging the vicinity of the sun by its redness, but now independent, and bearing

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