over violent motions, than he has over the rest *.

The third means of practice regards that grand engine, or instrument, both of nature and art, viz. heat and cold. And here the human power seems perfectly lame on one side; for we have the heat of fire infinitely stronger, or more intense, than that of the sun, as it naturally comes to us, or than the heat of animals; but cold is wanting, unless so far as it may be procured by the severity of winter, by caverns, or by the application of snow and ice, which in the way of comparison may about equal the degree of heat, afforded by the noon-day sun in some parts of the torrid zone, increased by the reverberations of mountains and walls; for such a degree of heat and cold may, for a small time, be endured by animals; but this is nothing to the heat of a melting furnace, or to a degree of cold that answers to such a degree of heat. And therefore all things with us tend but to rarifaction, desiccation, and consumption, and scarce any to condensation and inteneration or sup

*The experiments of this kind seem to have been no way duly prosecuted. The success which Mr. Hauksbee met with, in a slight attempt to destroy the spring of common air, might very well encourage the use of greater violence, stronger vessels, and a greater length of time, for the purpose. See his Physico-Mechanical Experiments, p. 162, &c.

spurious means.

pleness, unless by mixture and, as it were, by Wherefore instances of cold are with great diligence to be sought after, such as may perhaps be found by exposing bodies at great heights, in sharp frosts; laying them in subterraneal caves; surrounding them with snow and ice in deep places, or reservatories made for the purpose; by letting bodies down into wells; burying them in quicksilver and metals; plunging them in the waters which petrify wood *; bury`ing them in the ground (as they relate of the matter for making porcellane) and the like. So likewise the condensations naturally made by cold are to be sought, that their causes being 'discovered, such condensations may be transferred into arts. Such natural condensations we see in the sweating of marble and stone; in the dew condensed on the inside of glass windows after a frosty night; in the condensation of vapours into water within the earth, whence springs frequently arise; and other examples of this kind.

But beside those things which are cold to the touch, there are certain others potentially cold, which also condense, though they seem to ope

For producing the greatest degree of artificial cold, by freezing mixtures, see Mr. Boyle's History of Cold; and the chapter of fire, in Dr. Boerhaave's Chemistry.

rate only upon animal bodies, and scarce upon others. And of this kind are many things in medicine; for some remedies condense the flesh and tangible parts, such as astringents and thickners; and others condense the spirits, as appears chiefly in narcotics *.

There are two ways of condensing the spirits by soporiferous medicines; the one by appeasing the motion of the spirits; and the other by dispelling or putting them to flight. Thus violets, roses, lettuces, and the like mild and gentle things, by their friendly and moderately cooling vapours, invite spirits to unite and restrain their brisk and restless motion; but the stronger opiates, by a malignant and unfriendly quality, put the spirits to flight; and, therefore, if these are applied externally, the spirits presently retire from the part, and willingly enter into it no longer; but if taken internally, their fumes ascending to the head, every way chase away the spirits contained in the ventricles of the brain; and when the spirits thus retreat, and are unable to fly into any other part, they consequently come together, and are thus condensed, or sometimes quite extinguished or suffocated; though the same opiates taken in moderation, have the virtue by a secondary accident, (or by that con

* See the History of Life and Death.

densation, which succeeds upon the coming together of the spirits) of supporting and fortifying the spirits, and checking their useless and incentive motions; whence such opiates become of good service in the cure of diseases, and the prolonging of life*.

The preparations of bodies, likewise, for the admission or reception of cold, cannot be omitted. Thus it is thought that a little warming of water, hastens its freezing by cold, more than if the water was not warmed at all. And the instances of this kind are to be collected t.

But as nature supplies cold so sparingly, we should here imitate the apothecaries (who, when a simple cannot be procured, substitute one thing for another) and carefully search out the substitutes or succedaneums for cold; that is, we should enquire how condensations may be made in bodies, without cold, whose proper office it is to effect them.

And these condensations seem to be of four kinds; the first whereof depends the bare contrusion, which because of the resistance, or recoiling of bodies, has but little force in causing a permanent density, though it may do somewhat as an auxiliary. The second is made by

See the History of Life and Death. ✦ See Mr. Boyle's History of Cold.

the contraction of the grosser parts of a body after the avolation or exit of the finer, as happens in indurations by the fire, and the repeated quenching of metals, &c. The third is made by the approach or coming together of the more solid, or poderous, homogeneous parts of a body, which before were separated and mixed among the less solid; as in recovering the quicksilver from mercury-sublimate, which in powder possesses much more space than simple mercury; and so again, in purging and separating of metals from their dross. The fourth is made by consent, or applying such things as condense by a secret virtue in bodies, though these consents have hitherto seldom appeared, which is no wonder, because till some progress is made in the discovery of the forms and structures of things there can be but slender hopes of advantage arising from the enquiry into the consents of bodies*,

But with regard to the bodies of animals, there are doubtless many remedies, both internal and external, which condense, as it were, by consent, according to what was just now observed; but this kind of operation is rare in inanimate bodies t. There goes a report, as well in writ

* Because such consents, or particular agreements, depend thereon.

+ See the History of Condensation and Rarifaction,