HISTORY. 1. Air is simply dilated by heat for in this case there is nothing separated or emitted, as in tangible bodies; but barely an expansion made. 2. In the case of cupping-glasses, when the glass and the air it contains, are heated, the glass is applied to the skin; and soon after, the air which was dilated by the heat, gradually contracts itself, as the heat decreases; upon which the flesh is thrust into the glass by the motion of connexion*. If it be desired that the cupping-glass should draw stronger; let a sponge be dipt in cold water, and applied to the belly of the glass: for by this coolness, the internal air, will be more attracted, and the attraction of the glass increased+. 3. If a glass be heated, and inverted into water, it will attract the water; so as to fill a third part of the cavity: whence it is plain, that the air was rarified by the heat, in that proportion. But if, instead of a thin glass, which will not bear a great heat without danger of breaking; * See this motion explained in the Novum Organum, part ii. sect. ii. aph. 48. + This explanation in some measure holds, notwithstanding the present manner of accounting for effects of this kind, from the direct pressure of the air without ; and its rarification within. an iron or copper vessel were employed, and heated to a greater degree, we judge that air might be dilated above twice or thrice more; which is an experiment very well worth trying: as likewise, to ascertain the degree whereto the air may be rarified; that we may the better judge of its degree of rarifaction in the upper regions; and thence of the ether itselft. 4. It appears very plain, from the thermometer, that a small increase of heat may prodigiously expand the air; so that the hand laid upon the glass, a few rays of the sun, or even the breath of the by-standers shall affect it: nay, the tendencies of the external air to cold and heat, though imperceptible to the touch, do yet constantly dilate and contract the air in the glass*. 5. Hero describes an altar built so artificially, that when the offering is lit up thereon, water shall of a sudden descend, and put out the fire. No other contrivance is requisite to this purpose, than to leave a close hollow space under the altar, filled with air, which being heated by the fire, and consequently dilated, shall find no See Mr. Boyle's pneumatical experiments to this purpose. + See this weather-glass described, Novum Organum, part ii. aph. 13. exit but through a pipe rising along the wall of the altar; and having its mouth bent down at last, so as to discharge upon the altar. This upright pipe was filled with water; and had a belly in the middle, that it might contain the larger quantity; and a stop-cock at the bottom, to prevent the water from falling through; which stop-cock being turned, admitted the dilated air to rise up, and drive out the water.* 6. It was the invention of Fracastorius, to recover persons from apoplectic fits, by applying a heated metalline pan, at some distance, round the patient's head; in order to dilate, excite, and revive the spirits stagnating, congealed, or blocked up by the humours, in the cells of the brain, 7. Butterflies, and the like creatures, which lie for dead in the winter, recover motion and life by being warmed before the fire; or by the rays of the sun. And persons in fainting fits, are brought to themselves by taking, internally, such liquors as are spirituous and heating, as well as by external heat, friction, and motion, 8. Water opens or expands itself, in the following manner. With the first heat it emits a small and rarified vapour; without any other Here add the modern contrivance of making Jet d'Eaux, and fountains by the spring of compressed air. Upon continuance in its whole body, visible change in its body. of the heat, it does not rise nor in small bubbles, in the way of froth; but ascends in larger and rarer bubbles, and resolves itself into a copious vapour; which, if not ob structed, checked, or condensed, mixes with the air; being first visible, but afterwards diffusing itself, and becoming insensible. With the first heat, 9. Oil opens itself thus, certain little drops ascend; or small grains diffuse themselves through the body of the oil; and this with a small crackling noise: in the mean time, no bubbles play upon the surface, as in water; nor does the whole body swell, or emit any considerable exhalation. But, after some continuance, the whole body rises and dilates its self, very considerably; expanding, as it were to double the bulk and going off in a very copious and thick exhalation. This exhalation, if it does not take flame, at length mixes with the air; as does the vapour of water. But oil requires a greater degree of heat to make it boil; and begins to boil much slower than water.* 10. Spirit of wine rarifies, or opens itself, rather like water than oil: for it boils up in large * Lead melts at the bottom of oil, before the oil begins to boil. bubbles, without froth, or elevation of the whole body; but it expands and flies off with a much less degree of heat, and with much greater velocity, than water. It partakes both of an aqueous and oily nature: readily mixes with air; and suddenly takes flame. 11. Vinegar, verjuice, and wine, open themselves differently in this respect, that vinegar rises in smaller bubbles, and more about the sides of the vessel; but verjuice and wine in larger bubbles, and more in the middle of the vessel. 12. In general, unctuous liquors, as oil, milk, fat, &c. rise and swell in their whole body, at once; whilst ripe juices, (and unripe ones still more) rise in larger bubbles; but old and vapid juices, in smaller. 13. It is common for all liquors, even oil itself, before they boil, to throw, now and then, a few kind of half-bubbles about the sides of the vessel. 14. It is likewise common for all liquors to open themselves sooner, and to boil, and consume, in a small quantity, than in a large one. ADMONITION. The experiments about the opening of liquors should be made in glass vessels; that the motion in the body of the liquor may appear more |