within the mouth of the bladder, and tied it tight with a waxed thread; and then put the phial over hot coals in a chafing-dish. In a short time the vapour of the spirit of wine ascended into the bladder, and by degrees inflated it very strongly on every side. On this I immediately removed the glass from the fire, and pricked a hole in the top of the bladder with a needle, that the vapour might rather escape than return into drops. Then I took away the bladder from the phial, and examined by the scales how much of the half ounce of spirit of wine was gone and turned into air. The loss I found was not more than six pennyweights; so that six pennyweights of spirit of wine, which in the body (as I recollect) did not occupy a fortieth part of a pint, when turned into air filled a gallon.

Admonition. I recollect likewise that the bladder, on being removed from the fire, began to shrivel a little ; so that notwithstanding so remarkable an expansion, yet the vapour did not seem to be converted into a pure and fixed pneumatic body, seeing it was inclined to recover itself. Nevertheless this experiment may prove fallacious, if we conjecture from this that common air is still rarer than this kind of vapour. For I conceive that spirit of wine made. pneumatic (though not pure), yet by reason of its heat exceeds cold air in rarity, because air itself is wonderfully dilated by heat, and considerably exceeds cold air in bulk. I suppose therefore that if the experiment were made with water the expansion would be much less; though the body of water contains more matter than the spirit of wine.

3. If you look at the fume rising from a wax candle

ust put out, and measure its thickness by the eye; and again, if you observe the body of that fume when it is rekindled; you will see that the expansion of the flame, as compared with the fume, is about double.

Admonition. If you take a few grains of gunpowder and set them on fire, there is a great expansion compared with the body of the powder. But on the other hand, when the flame is extinguished the body of the fume expands much more. Do not however conceive from this that a tangible body is more expanded in fume than in flame; for it is quite the reverse. The reason of the appearance is, that flame is a body entire, and fume a body mixed in far the greater part with air; and therefore as a little saffron colours a large quantity of water, so a little fume spreads itself over a large space of air. For the fume when thick (as has been said before) and not diffused, appears less than the body of flame.

4. If you take a piece of orange peel (which is aromatic and oily) and squeeze it suddenly near a candle, there spirts out a kind of dew in small drops; which nevertheless makes a very large body of flame as compared with the drops.

Observation.

The conceit of the Peripatetics, that the variety of the elements compared one with the other is in a proportion of ten to one, is a thing fictitious and arbitrary. For it is certain that air is at least a hundred times rarer than water, and flame than oil; but that flame is not ten times rarer than air itself.

Admonition.

Let it not be thought that this inquiry and speculation on pneumatic bodies is too subtle or curious. For it is certain that the omission and neglect hereof have paralysed philosophy and medicine, and made them as it were planet-struck; so that they have stood amazed and helpless as far as the true investigation of causes is concerned; attributing to qualities things which are owing to the spirits; as will appear more fully in the proper title of Pneumatic Bodies.

OF THE DILATATIONS AND CONTRACTIONS OF BODIES.

Transition.

So much for the inquiry concerning the bulk of matter in bodies, according to their different consistencies, while they are at rest. But concerning the appetite and motion of bodies, whereby they swell, subside, become rarefied, condensed, dilated, contracted, and occupy more or less space, we must inquire, if possible, still more accurately. For this inquiry is more profitable, as it both reveals and governs nature. Nevertheless it must here be made by snatches, and cursorily; for this title of Dense and Rare is so general, that if it were fully drawn out it would anticipate many of the succeeding titles, which is not fit to be done.

Admonition. It would not be difficult for me to reduce the scattered history (which I shall now subjoin) to a better order than that which I have followed, by placing instances which are related to one another by themselves. But I have purposely avoided this, for two reasons. First, because many

Be it

of the instances are of a doubtful nature, and bear upon more than one subject; and therefore accurate order in such things involves either iteration or error. Secondly (and this is the principal reason why I am averse from any exact method), I wish to leave the matter in hand open for every man's industry to imitate. Now if this collection of instances had been arranged according to any scientific and remarkable method, many doubtless would have despaired of being able to make an inquiry of the same kind. By example therefore, as well as by admonition, I warn every man to make use, in procuring and propounding instances, of his own judgment, his own memory, and his own store. enough that invention always proceeds by writing, and not by memory (for that would be something ludicrous in such a variety of instances); so that it may afterwards be perfected by the light of true induction. And let it be ever kept in mind that in this work I only demand a contribution and tax from the sense for the treasury of the sciences; and that I am not proposing examples for the illustration of axioms, but experiments to establish them. But yet in setting forth the instances I shall not neglect arrangement altogether, nor proceed loosely, but I shall so place them that they may mutually shed light on one another.

Scattered History.

1. No wonder if dilatation of a body follows on the reception of another body within it; for this is a direct augmentation or addition, not a true rarefaction. Nevertheless, when the body admitted is a pneumatic

body (as air or spirit), or even when it is a tangible body, if it glide in and insinuate itself gradually, it is commonly regarded as rather a swelling than an addition.

DILATATIONS BY SIMPLE INTROCEPTION, OR THE ADMISSION OF A NEW BODY.

2. Bladders and other tensile bodies (as bellows for instance) are inflated and distended by air alone; so that they become hard, and will bear to be struck and tossed about. A bubble of water also is like a bladder, except that it is so fragile.

3. Liquors poured from above out of one vessel into another, or stirred up violently with spoons, ladles, or winds, are mixed up and united with the air, and thereby rise into froth. But they soon subside and shrink into less space, the air escaping as the little bubbles of froth burst.

4. Children build towers of bubbles from soap and water (the soap making the water more tenacious); so that a very little water, by the introception of air, fills a large space.

5. But it is not found that flame can be mixed with air, and grow frothy by the blowing of bellows or any other agitation from without, so as to constitute a body compounded of flame and air; like froth, which is compounded of air and liquor.

6. But on the other hand it is certain that, by an internal mixture in a body before it is set on fire, a mixed body may be made of air and flame. For gunpowder has uninflammable parts by reason of the nitre, and inflammable parts principally by reason of the sul phur; whence likewise its flame is whiter and paler