keeps water fluid, another turns it into elaftic air (a). And air itself seems to be nothing else but vapours and exhalations, rendered elastic by fire. Nothing flames but oil: and fulphur with water, falt, and earth compofe oil; which fulphur is fire therefore fire enclosed attracts fire, and causeth the bodies whofe compofition it enters to burn and blaze.

196. Fire collected in the focus of a glafs operates in vacuo, and therefore is thought not to need air to fupport it. Calx of lead hath gone off with an explofion in vacuo, which Niewenty't and others take for a proof that fire can burn without air. But Mr. Hales attributes this effect to air enclosed in the red lead, and perhaps too in the receiver, which cannot be perfectly exhaufted. When common lead is put into the fire in order to make red-lead, a greater weight of this comes out than was put in of common lead. Therefore the red-lead fhould feem impregnated with fire. Mr. Hales thinks it is with air. The vaft expansion of compound aqua fortis, Mr. Niewenty't will have to proceed from fire alone. Mr. Hales contends that air muft neceffarily co-operate. Though by Niewenty't's experiment it fhould feem, the phofphorus burns equally, with and without air.

197. Perhaps they who hold the oppofite fides in this question, may be reconciled by obferving that air is in reality nothing more than particles of wet and dry bodies volatilised, and rendered elaftic by fire (b). Whatever therefore is done by air must be afcribed to fire, which fire is a fubtile invifible thing, whofe operation is not to be difcerned but by means of fome groffer body, which

(a) 149.

(b) 147, 150, 151. M 2

ferves

ferves not for a pabulum to nourish the fire, but for a vehicle to arreft and bring it into view. Which feems the fole use of oil, air, or any other thing, that vulgarly paffeth for a pabulum or food of that element.

198. To explain this matter more clearly, it is to be obferved, that fire, in order to become fenfible, must have fome fubject to act upon. This being penetrated and agitated by fire affects us with light, heat, or fome other fenfible alteration. And this fubject fo wrought upon may be called culinary fire. In the focus of a burning glafs expofed to the fun, there is real actual fire, though not difcerned by the fenfe, till it hath fomewhat to work on, and can fhew itself in its effects, heating, flaming, melting, and the like. Every ignited body is, in the foregoing fenfe, culinary fire. But it will not therefore follow, that it is convertible into pure elementary fire. This, for ought that appears, may be ingenerable and incorruptible by the courfe of nature. It may be fixed and imprifoned in a compound (a), and yet retain its nature, though loft to fenfe, and though it return into the invifible elementary mafs, upon the analyfis of the compounded body: as is manifeft in the folution of ftone lime by water.

199. It fhould feem, therefore, that what is faid of air's being the pabulum of fire, or being converted into fire, ought to be understood only in this fenfe, to wit, that air being lefs grofs than other bodies, is of a middle nature, and therefore more fit to receive the impreffions of a fine ætherial fire (b), and impart them to other things. According to the antients, foul ferveth for a vehicle to

(a) 169, 192, 193.

(b)163.

in

intellect (a), and light or fire for a vehicle to the foul; and, in like manner, air may be fuppofed a vehicle to fire, fixing it in fome degree, and communicating its effects to other bodies.

200. The pure invisible fire or æther doth permeate all bodies, even the hardest and most folid, as the diamond. This alone, therefore, cannot, as some learned men have fuppofed, be the cause of mufcular motion, by a mere impulfe of the nerves communicated from the brain to the membranes of the muscles, and thereby to the enclosed æther, whofe expansive motion, being by that means increafed, is thought to fwell the muscles, and cause a contraction of the fleshy fibres. This, it fhould feem, the pure æther cannot do immediately, and of itself, because, fuppofing its expansive motion to be increased, it must ftill pass through the membranes, and confequently not swell them, inafmuch as æther is fuppofed freely to pervade the most solid bodies. It fhould feem therefore, that this effect must be owing, not to pure æther, but to æther in fome part fixed and arrested by the particles of air.

201. Although this æther be extremely elastic, yet as it is fometimes found by experience to be attracted, imprisoned, and detained in grofs bodies (b), fo we may fuppofe it to be attracted, and its expanfive force diminished, though it should not be quite fixed, by the loofe particles of air, which combining and cohering therewith may bring it down, and qualify it for intercourfe with groffer things, Pure fire may be faid to animate air, and air other things. Pure fire is invifible; therefore flame is not pure fire. Air is neceffary both to life and flame. And it is found by experi

(a) 178.

(b) 169.

ment,

ment, that air lofeth in the lungs the power of feeding flame. Hence it is concluded, that the fame thing in air contributes both to life and flame. Vital flame furvives culinary flame in vacuo: therefore it requires lefs of that thing to fuftain it.

202. What this may be, whether fome certain proportion, or fome peculiar parts of æther, is not eafy to fay. But thus much feems plain, that whatever is afcribed to acid may be alfo afcribed to fire or æther. The particles of æther fly afunder with the greatest force: therefore, agreeably to Sir Ifaac Newton's doctrine, when united they muft attract each other with the greateft force. Therefore they conftitute the acid. For whatsoever ftrongly attracts and is attracted, may be called an acid, as Sir Ifaac Newton informs us in his tract De acido. Hence it fhould feem, that the fulphur of Homberg, and the acid of Sir Ifaac are at bottom one and the fame thing, to wit, pure fire or æther.

203. The vital flame or ethereal spirit, being attracted and imprisoned in groffer bodies, feemeth to be fet free and carried off by the fuperior attraction of a fubtil and pure flame. Hence, perhaps, it is that lightening kills animals, and turns fpirituous liquors vapid in an inftant.

204. Hippocrates, in his book concerning the Heart, obferveth, that the foul of man is not nourifhed by meats and drinks from the lower belly, but by a pure and luminous substance, darting its rays and diftributing a non-natural nourishment, as he terms it, in like manner as that from the inteftines is diftributed to all parts of the body. This luminous non-natural nourishment, though it be fecreted from the blood, is exprefly faid not to come from the lower belly. It is plain, therefore,

he

he thought it came into the blood either by refpiration, or by attraction through the pores. And it must be acknowledged, that fomewhat igneous or æthereal brought by the air into the blood feems to nourish, though not the foul itself, yet the interior tunicle of the foul, the auraï fimplicis ignem.

205. That there is really fuch a thing as vital flame, actually kindled, nourished, and extinguished like common flame, and by the fame means, is an opinion of fome moderns, particularly of Doctor Willis in his tract De fanguinis accenfione: that it requires conftant eventilation, through the trachea and pores of the body, for the difcharge of a fuliginous and excrementitious vapour: and that this vital flame, being extremely fubtil, might not be feen any more than fhining flies or ignes fatui by day-light. And yet it hath fometimes become vifible on divers perfons, of which there are undoubted inftances. This is Dr. Willis's notion: and perhaps there may be fome truth in this, if it be fo understood, as that light or fire might indeed constitute the animal fpirit or immediate vehicle of the foul.

206. There have not been wanting those, who, not content to fuppofe light the most pure and refined of all corporeal beings, have gone farther, and bestowed upon it fome attributes of a yet higher nature. Julianus the Platonic philofopher, as cited by Ficinus, faith, it was a doctrine in the theology of the Phoenicians, that there is diffufed throughout the universe, a pellucid and fhining nature pure and impaffive, the act of a pure intelligence. And Ficinus himself undertakes to prove, that light is incorporeal, by feveral arguments: Because it enlightens and fills a great space in an inftant, and without oppofition: Because several lights