THE

MONTHLY REVIEW,

For JANUARY, 1760.

The Nature, Properties, and Laws of Motion of Fire discovered and demonftrated, by Obfervations and Experiments. By William Hillary, M. D. 8vo. 2s. Davis and Reymers.

INCE the establishment of the Newtonian Philofophy,

it has been the constant custom of phyfical Writers, of a fecond-rate genius, to decry all attention to fyftems and hypothefes, as chimerical and ufelefs: experiment alone being, by them, held fufficient to direct us in the investigation of the feveral phenomena of Nature.

That experiment is abfolutely neceffary to our affiftance, cannot be denied; but, unless the genius and fagacity of the Obferver, in directing his enquiries, and drawing juft conclufions from obfervation, be equal to his accuracy and induftry in making experiments, we will venture to fay, he is full as likely to be miffed himfelf, and to mislead others, in the way of analyfis, as thofe who proceed in a synthetical method only.

The errors afifing from falfe conclufions drawn from experiment, are alfo the more pernicious to fcience, as they are fuch as the Obferver will the more obftinately perfift in, on the mistaken notion of his having experimental proof of what he maintains: whereas a certain diffidence generally attends opinions founded on mere ratiocination. The Hypothefifts VOL: XXII.

B

have

have also this on their fide; that however falfe their systems may prove in the end, they fhew, for the most part, fome marks of genius in their inventors; while a farrago of undigefted experiments, however ufeful they may prove in the affiftance of others, ferves rather as a monument of industry and application, than as any proof of ingenuity in the maker of them.

Perhaps at this juncture, the farther improvement of Natural Philofophy requires rather a theoretical genius than a laborious obferver: for certain it is, that we have more accurate experiments already made, than are reduced to any fyftem, or are to be easily reconciled to each other.

As there is no ftudy, however, more generally pleafing to individuals than that of Phyfics, fo there are no discoveries more important and ufeful to Society, than those which are the objects of this fcience, and which are frequently the unlooked for, and casual, effects of experimental enquiries.

Every rational attempt, therefore, to inveftigate the phenomena of natural bodies, their properties, and laws of motion, as it is an employment becoming both the Philofopher and the Citizen, fo it lays an indifputable claim to the gratitude of the public. Its admiration and applaufe, indeed, if fuch attempts prove fuccefsful, the Phyfiologift will, fooner or later undoubtedly acquire; but, if it happen otherwise (and otherwise it often must happen, in refearches of fo complex and intricate a nature) to what mortification is he too frequently fubjected, in return for his well-meant, but unfuccefsful endeavours!

In what degree Dr. Hillary, of whofe medical knowlege we lately exprefled a juft efteem, may meet with approbation, or applause, proportionable to the merit of his defign in the tract before us, we do not pretend to determine; but, as the fubject is particularly curious and interefting, the duty in which we conceive ourselves bound to the public, calls upon us to fhew, how far he appears to us to have fucceeded in the execution of that defign.

We are told, in the introduction to this performance, that the Author's motive and defign, in entering on his enquiries into the Nature and Properties of Fire, were to fupply what the celebrated Boerhaave left undiscovered, as to this fubject. For that, although that learned Profeffor did difcover most of its fubtle properties, yet he had not proceeded fo far as to eftablish its Laws of Motion. This, therefore, induced our

Author

Author to attempt a difcovery of those laws, and to endea your to establish them as fuch.

But, as he found, by experiments, that most of the Properties of Fire, and all its modes of moving and acting, were fo different from, and fome of them contrary to, the known Laws of Motion of all other matter, it often caufed him (not unreasonably) to doubt their being true. And feeing farther, that the very name of new Laws of Motion, of any kind of matter, would probably be thought a fufficient reason for rejecting them (efpecially as it is very generally fuppofed, that the Laws of Motion difcovered by Newton, are fufficient to account for the motions and actions of all material bodies) Dr. Hillary confeffes himself to have been frequently difcouraged in his purfuit: but the ftill prevailing defire of obtaining farther information on this fubject, induced him to reaffume his experiments, till he had obtained a fatisfactory knowlege of its properties, and fingular modes of motion.

After a very careful and attentive perufal, however, of the Doctor's performance, we are ftill apt to be of opinion, that notwithstanding the principles of the Newtonian Philofophy may not fufficiently enable us to account for fome of the more occult properties of bodies, yet no material bodies whatever act contrary to the laws of motion he has eftablished and demonftrated. But to come to particulars. -Our Author's first propofition is this,

Prop. I. Fire is a Being which exifts in all places, or in every part of space in the whole univerfe.'

• That

This propofition is thus attempted to be proved. Fire exifts, though often unperceived by any of our fenfes, ⚫ and in a confiderable quantity too, in every part of this ter reftrial globe, even in the coldeft fubpolar regions which have been yet difcovered, and which men have been able to endure, is evident from the following fimple experiment, • among several others: nay, the greatest and hottest degree of Fire may be inftantly collected out of the coldest air, in 'the coldeft regions, by the motion and attrition of one hard body against another.

The hottest and greatest degree of Fire may be instantly collected in Greenland, Spitfbergen, Iceland, or in Tartary, folely by the collition and attrition of a piece of flint against a piece of fteel, which in a moment burns and melts the abraded particles of the flint and fteel into glass; and yet the greatest and hotteft degree of Fire which human B 2

• art

art can make with the best fewel, will not burn fuch sma abraded parts of flint and steel into glass in so short a space • of time.

Let that fpark of Fire fo collected, be put to a great quantity of the beft and drieft fewel, in that cold place, and a prodigious great quantity of Fire will foon be col•lected, and will burn with a prodigious great force.

Here all this great quantity of Fire, which was thus foon collected, exifted in a ftill ftate of equilibrium in the circumambient cold air, and in the adjacent earth and ice in that cold place, at that time, the fun being then below the horizon, fo that no fire could be emitted from it, or be collected from it then at that place. Neither was the fire new created, for poor impotent man can create nothing; but was only collected by the motion and attrition of the flint and fteel against each other; and was continually collected afterwards and increased by the motion and attrition of the conftituent particles of the fewel and the elements of the fire upon and against each other, which fo continued to act upon each other, till the elementary parts of the fewel were all confumed, and diffipated or carried off with the fire, as it returned into the air and earth again from whence it came, and was reftored to its ftate of equilibrium and reft as it was before, where it would always remain at reft, if it was neither collected again by the motion of other bodies, nor put in motion by the directing power of light from 'the fun.'

In answer to this however, we may venture to affert, that the fire here fpoken of might be really created: for poor impotent man can ftrike a light, and burn a pile of faggots, as well as play on the violin, or beat a drum: the found and fire thereby ereated being, both equally, the effects of his action; and, perhaps the one juft as much a material Being as the other. By the one kind of action the parts of bodies are put into fuch a motion as to give the fenfation of heat and appearance of fire; and by the other into fuch a motion as gives the fenfation of found."

If Fire alfo be a folid body, as our Author afferts, and is only collected in fuch a cafe as the above, its degree of heat fhould neceffarily follow its quantity: but we fee a very small quantity of this fire capable of producing a more intenfe degree of heat than the largeft quantity of it otherwife difpofed. Perhaps, in fact, a very fmall quantity of any kind of matter, moving or ftriking against any other quantity of it, with a propor

tionable

tionable velocity, would generate fire, to any degree of heat; tho' we have no reafon to conclude the greateft quantity, of any kind or species of it whatever, would produce that phenomenon, to the like intenfity of heat, if not fo put in motion. Suppofing, therefore, all that quantity of matter which our Author calls fire, and conceives to be collected in the above cafe, to have existed in a state of reft before the collifion of the flint and fteel, it were, in our opinion, very improper to call it Fire, either before it was actually attracted, and put in motion, by that collifion, or after the fewel was confumed, and that matter returned (as our Author conceives) to its former ftate of rest *.

Befides, if Fire be a body, and confifts of perfectly folid elements, how is it poffible for the fimple collifion of the flint and fteel to collect fuch a quantity of it, as we must fuppofe neceffary to occafion fuch an intenfe degree of heat, in fo fmall a space? and in fo fhort a time? And how comes it, that the accumulation of a much greater quantity did not produce a much greater degree of heat? Certainly the intenfity of heat followed the motion, and not the quantity even of this fuppofed fire.

Again, if fire, at reft, be diffufed equably throughout all fpace, and only appear to burn in any part of it, by its accumulation, it should follow, that in the space furrounding any collected body of fire, it fhould be colder than if fuch a body had not been collected; becaufe, in proportion to the quantity accumulated in one place, must be the privation of it in others. And thus, notwithstanding the heat the planets receive from the fun, they would, according to this fyftem, have been, on the whole, warmer had there been no fun at all.

But, perhaps, it will be faid, that tho' Fire is a real body, yet it does not give heat, unlefs put in motion. This, however, is contrary to the tenour of our Author's reafoning, who proves the existence of fire by its effects; i. e. the heat of bodies. Now if, after conceiving the exiftence of fire as a body, we are ftill under the neceffity of fuppofing it must be put in motion, before it produce the effect by which its existence is known, have we not fufficient reafon to conclude, agreeable to Sir Ifaac Newton's opinion, that Fire is nothing more than the inteftine motion of the parts of heated bodies? and that the intenfity of fuch heat is proporB 3 tionable

Thus, it would be improper to call a piece of Charcoal Fire, before it were red-hot, or after it thould be reduced to afhes, by

burning;