VACUUM, in philosophy, denotes a space empty, or devoid, of all matter or body. It has been the opinion of some philosophers, particularly the Cartesians, that nature admits not a vacuum, but that the universe is entirely-f & of matter : in consequence of which opinion they were obliged to assert, that if every thing con tained in a vessel could be taken out or annihilated, that sides of the vessel, how ever strong, would come together ; but this is contrary to experience, for the greatest part of the air may be drawn out of a vessel by means of the air-pomp, not withstanding which it will remain whole, if its sides are strong enough to support the weight of the incumbent atmosphere. Should it be objected here, that it is im possible to extract all the air out of a ves sel, and that there will not be a vacuum on that account ; the answer is, that since a very great part of the air that was in the vessel may-be drawn out, as appears by the more quick descent of light bodies in a receiver when exhiusted of its air, there must be some vacuities between the parts of the. remaining air ; which is sufficient to constitute a vacuum. Indeed, to this it may be objected by a Cartesian, that those vacuities are filled with mate ria subtilis, that passes freely through the sides of the vessel, and gives no resist ance to the foiling bodies : but as the ex istence of this materia subtilis can never be proved, we are not obliged to allow the objection, especially since Sir Isaac Newton has &Ind that all matter affords 'a resistance' nearly in proportion to its density. There are many otherarguments
to prove this, particularly the motions of the comets through the heavenly regions, without any sensible resistance ; the dif ferent weight of bodies of the same bulk, &c. All the parts of spaces, says Sir Isaac Newton, are not equally full ; for if they were, the specific gravity of the fluid which would fill the region of the could not, by reason of the exceeding great density of its matter, give way to the specific gravity of quicksilver, gold, or any body, how dense soever ; whence neither gold, nor any other body, could 'descend in the air ; for no body can de scend in a fluid, unless it be specifically heavier than it. But if a quantity of mat ter may, by rarefaction, be diminished in a given space, why may it not diminish in infinitum ? And if all the solid particles of bodies are of the same denSity, and cannot be rarified, without leaving pores, there must be a vacuum.