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different juices from the common mafs. The fame holds alfo with regard to the capillary veffels (a) of vegetables, it being evident that through the fine ftrainers in the leaves and all over the body of the plant, there be juices or fluids of a particular kind drawn in, and feparated from the common mafs of air and light. And that the most elaborate fpirit, whereon the character or diftinguishing virtue and properties of the plant depend, is of a luminous (b) and volatile nature, being loft or escaping into air or æther, from effential ails and odoriferous waters, without any fenfible diminution of the fubject.

216. As different kinds of fecreted light or fire produce different effences, virtues, or specific properties, fo alfo different degrees of heat produce different effects. Thus one degree of heat keeps the blood from coagulating, and another degree coagulates the blood. Thus a more violent fire hath been obferved to fet free and carry off that very light, which a more moderate fire had introduced and fixed in the calcined regulus of antimony. In like manner, one kind or quantity of this ætherial fiery fpirit may be congenial and friendly to the fpirits of a man, while another may be noxious.

217. And experience fheweth this to be true. For the fermented fpirit of wine or other liquors produceth irregular motions, and fubfequent depreffions in the animal fpirits. Whereas the luminous fpirit lodged and detained in the native bal fam of pines and firs, is of a nature fo mild and benign and proportioned to the human constitution, as to warm without heating, to cheer but not ine

(a) 30, 31, 33, 35,

(4) 37 43.

briate,

briate, and to produce a calm and fteddy joy like the effect of good news, without that finking of fpirits which is a fubfequent effect of all fermented cordials. I may add, without all other inconvenience, except that it may like any other medicine be taken in too great a quantity for a nice ftomach. In which cafe it may be right, to leffen the dofe, or to take it only once in the four and twenty hours, empty, going to bed (when it is found to be leaft offenfive) or even to fufpend the taking of it for a time, till nature fhall feem to crave it, and rejoice in it's benign and comfortable spirit.

218. Tar-water ferving as a vehicle to this fpirit is both diuretic and diaphoretic, but feems to work it's principal effect by affifting the vis vitæ, as an alterative and cordial, enabling nature by an acceffion of congenial fpirit, to affimilate that which could not be affimilated by her proper force, and fo to fubdue the fomes morbi. And this should feem in most cafes the best and safest course. Great evacuations weaken nature as well as the disease. And it is to be feared that they who use falivations and copious bleedings may, though they fhould recover of the diftemper, in their whole life be never able to recover of the remedies.

219. It is true indeed, that in chronical cafes there is need of time to compleat a cure, and yet I have known this tar-water in diforders of the Jungs and stomach to prove a very speedy remedy, and to allay the anxiety and heat of a fever in an inftant, giving eafe and fpirits to the patient. This I have often experienced, not without furprise at seeing these falutary effects follow fo immediately in a fever on taking a glass of tar-water. Such is the force of thefe active vivifying princi ples contained in this balsam,

220. Force

220. Force or power, ftrictly speaking, is the agent alone who imparts an equivocal force to the invifible elementary fire, or animal spirit (a) of the world, and this to the ignited body or visible flame, which produceth the sense of light and heat. In this chain the first and last links are allowed to be incorporeal: the two intermediate are corporeal, being capable of motion, rarefaction, gravity, and other qualities of bodies. It is fit to distinguish thefe things, in order to avoid ambiguity concerning the nature of fire.

221. Sir Ifaac Newton in his Optics, afks; Is not fire a body heated fo hot as to emit light copioufly? for what else, adds he, is a red hot iron than fire? Now it fhould feem, that to define fire by heat, would be to explain a thing by it felf.. A body heated fo hot as to emit light is an ignited body, that is, hath fire in it, is penetrated and agitated by fire, but is not it felf fire. And although it fhould in the third foregoing acceptation, or vulgar fenfe pafs for fire, yet it is not the pure elementary (b) fire in the fecond or philofophic fenfe, fuch as was understood by the fages of antiquity, and fuch as is collected in the focus of a burning glafs; much less is it the vis, force, or power of burning, destroying, calcining, melting, vitrifying, and raifing the perceptions of light and heat. This is truly and really in the incorporeal agent, and not in the vital fpirit of the universe. Motion, and even power in an equivocal ¡fense, may be found in this pure æthereal fpirit, which ignites bodies, but is not itfelf the ignited body, being an inftrument or medium (e) by which the real agent doth operate on groffer bodies..:

(a) 153, 156, 157

(b) 190. (*) 160.

222. It

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222. It hath been fhewed in fir Ifaac New ton's Optics, that light is not reflected by imping ing on bodies, but by fome other caufe. And to him it seems probable, that as many rays as im pinge on the folid parts of bodies, are not reAlected but ftifled and retained in the bodies. And it is certain, the great porofity of all known bodies affords room for much of this light or fire to be lodged therein, Gold it felf the most folid of all metals, feems to have far more pores than folid parts, from water being preffed through it in the Florentine experiment, from magnetic effluvia paffing, and from mercury entering its pores fa freely. And it is admitted that water, though im poffible to be compreffed, hath at leaft. forty times more pores than folid parts, And as acid par ticles, joined with thofe of earth in certain proportions, are fo closely united with them, as to be quite hid and loft to all appearance, as in mercurius dulcis and common fulphur, fo alfo may we conceive the particles of light or fire to be absorbed and latent in groffer bodies.

223. It is the opinion of fir Ifaac Newton, that fomewhat unknown remains in vacuo, when the air is exhaufted. This unknown medium he calls æther. He fuppofeth it to be more fubtil in its: nature, and more fwift in its motion, than light, freely to pervade all bodies, and by its immenfe elasticity to be expanded throughout all the hea-1 vens. Its denfity is fuppofed greater in free and. open spaces, than within the pores of compact bodies. And, in paffing from the celeftial bodies. to great distances, it is fuppofed to grow. denfer and denfer continually; and thereby cause thosei great bodies to gravitate towards one another, and their refpective parts towards their centers, every

body

body endeavouring to pafs from the denfer parts of the medium towards the rarer.

224. The extreme minutenefs of the parts of this medium and the velocity of their motion, together with its gravity, denfity, and. elaftic force, are thought to qualify it for being the cause of all the natural motions in the univerfe. To this cause are afcribed the gravity and cohesion of bodies. The refraction of light is also thought to proceed, from the different density and elastic force of this ætheriał medium in different places. The vibrations of this medium alternately concurring with, or obftructing the motions of the rays of light, are fuppofed to produce the fits of eafy reflexion and tranfmiffion. Light by the vibrations of this medium is thought to communicate heat to bodies. Animal motion and fenfation are alfo accounted for by the vibrating motions of this ætherial medium, propagated through the folid capillaments of the nerves. In a word, all the phænomena and properties of bodies, that were before attributed to attraction, upon later thoughts feem afcribed to this æther, together with the various attractions themselves.

225. But in the philofophy of fir Ifaac Newton, the fits (as they are called) of easy tranfmiffion and reflexion, seem as well accounted for by vibrations excited in bodies by the rays of light, and the refraction of light by the attraction of bodies. To explain the vibrations of light by thofe of a more fubtil medium, feem an uncouth explication. And gravity feems not an effect of the density and elafticity of æther, but rather to be produced by fome other caufe; which fir Ifaac himself infinuates to have been the opinion even of thofe ancients who took vacuum, atoms, and the gravity of atoms for the principles of their philofophy, tacitly attri

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