VACUUM, or Vacuum Boyleanum, is also used to express that approach to a real vacuum which we are supposed to arrive at by means of the air-pump. See AIR-PUMP. Thus, any thing put in a receiver so exhausted, is said to be put in vacuo; and thus most of the experiments with the air-pump, are performed in vacuo, or in vacuo Boyleano.
Some of the principal phenomena observed of bodies in vacuo are, that the heaviest and lightest bodies, as a guinea and a feather, fall here with equal velocity: That fruits, as grapes, cherries, peaches, apples, &c. kept for any time in vacuo, retain their nature, freshness, colour, &c. and those withered in the open air, recover their plumpness in vacuo:—All light, and fire, becomes immediately extinct in vacuo:—The coalition of flint and steel in vacuo produces no sparks:—No sound is heard even from a bell rung in vacuo:—A square viol, full of common air, well closed, breaks in vacuo; a round one does not:—A bladder half full of air, will heave up forty pound weight in vacuo:—Cats, and most other animals, readily expire in vacuo.
By experiments made in 1704, Mr Derham found,
that animals which have two ventricles, and no foramen ovale, as birds, dogs, cats, mice, &c. die in less than half a minute; counting from the first exsufflation: a mole died in one minute, a bat lived seven or eight.—Insects, as wasps, bees, grasshoppers, &c. seemed dead in two minutes; but, being left in vacuo 24 hours, came to life again in the open air: snails continued 24 hours in vacuo, without appearing much concerned.
Seeds planted in vacuo do not grow:—Small-beer dies, and loses all its taste in vacuo:—Lukewarm water boils very vehemently in vacuo:—Air, rushing through mercury into a vacuum, throws the mercury in a kind of shower upon the receiver, and produces a great light in a dark room.
The air-pump can never produce an entire extraction of the air, as is evident from its structure and the manner of its working: in effect, every exsufflation only takes a part of the air; so that there will still be some left after any finite number of exsufflations.—Add, that the air-pump has no longer any effect, than while the spring of the air remaining in the receiver is able to lift up the valves: when the rarefaction is come to that degree, you can come no nearer to a vacuum. Sir Isaac Newton, observing that a thermometer suspended in vacuo, and in that state removed to a warm or a cold room, receives the heat or cold, rises or falls, almost as soon as another in open air, takes thence occasion to suspect that the heat of the warm room is conveyed through the vacuum by the vibrations, of a much subtler medium than air, which remained in the vacuum after the air was drawn out.