Again : As all bodies placed In a very foiid air, do, 
by degrees, grow cold, motionlefs, rigid, &c. i. e. 
-though there be ftill feme remains of fire, and in 
proportion*as that is diminifhed, the effect is accele- 
rated ; it follows, that cold, a lefs degree of heat, is 
the effed of a leffer adion of fire : and all adion rifes 
apparently from the fame fource. 
Then, as fire can render the moll foiid. bodies, as 
done, metals, &c. (as appears very evident in large 
burning-glades, in which gold itfelf immediately cal- 
cines, and emits fumes, i. e. becomes fluid) fo the 
want of fire would convert the moft fluid bodies, as 
fpirits of -wine, &c. into folids. 
Fire is diftinguifhed into two kinds, called elemen- 
tary or pure fire, which is fuch as exifls in itfelf, and 
alone is properly called fire ; or common or culinary 
fire, which is raifed and kindled from the former, and 
is that which agitates and affeds ignited, combuftible, 
and moveable bodies, the particles of which, joining 
with thofe of the pure fire, conftitute pure flame. 
This latter is improperly called fire, in that not only 
a fmall part of it is real or pure fire; and in ig- 
nited bodies, that which flames, fmokes, &c. is not 
Amply fire ; whereas pure fire, fuch as is colleded 
in a burning-glafs, yields no flame, fmoke, afhes, or 
the like. 
Fire may be prefent in the greateft abundance, yet 
without any heat : this is evident in the tops of the 
higheft mountains, illuminated by the fun, where the 
cold is always extremely pinching, and this even un- 
der the equator, there being mountains there which 
are perpetually covered with fnow, though there can 
be no want of fire. 
So a large burning-glafs has no effed : the fmalleft 
warmth cannot be felt in its focus in a place where 
the fun does not fhine, or when the fun is covered 
with a cloud, but a piece of metal may be feen to 
melt the very moment the fun emerges. 
Fire may be in exceeding fmall quantity, and yet 
burn with great violence : thus fpirit of wine when 
fet on fire, does not burn the hands ; and though 
poured on a piece of red-hot iron, does not take fire; 
fo that the fire that is in, fliould not appear very 
great : yet if it meet with fome harder body while it 
is burning, the particles of which body it is capa- 
ble to agitate by the attrition of its own, it will yield 
a fierce flame, capable of burning a harder body than 
the hand. 
From this it appears, that the relation of heteroge- 
neous particles, agitated by the fire, has more effed 
in refped to heat than the adion of the fire Itfelf : 
nor need we be far to feek for the mechanical reafon 
of this, for the particles of fire, being all equal and 
fpherical, mufl of themfelves be harmlefs ; but if 
they carry certain fpicula, or any other bodies along 
with them, then they become capable of doing much 
harm. 
Hence, though the flame of a piece of wood may 
give a fenfe of heat, and burn fuch things as are ap- 
plied to it, it does not therefore neceflarily follow, 
that there is any pure fire in it, fo that the dif- 
tindion of pure and common fire is abfolutely ne- 
ceffary : though this diftindion has been overlooked 
by moft or all the authors before Dr. Boerhaave, who 
have written on fire ; which has led them into egre- 
gious miftakes, infomuch that moft of them have held, 
that the flame of & piece of wood is all fire, which ap- 
pears to be falfe from what has been already faid, and 
alfo what follows. 
Elementary or pure fire is of itfelf imperceptible, and 
only difcovers itfelf by certain effeds that it pro- 
duces in bodies, and thefe effeds are only to be learnt 
by the changes which arife in bodies. Thefe effeds 
are three; ift, heat; 2dly, dilatation in all foiid 
bodies, and rarefadion in all fluids ; 3dly, motion. 
The firft effed of elementary fire on bodies is heat : 
heat arifes wholly from fire, and in fuch a manner, 
that the meafure of heat is always the meafure of 
fire ; and that of fire, of heat ; fo the heat is infepa- 
rable from the fire. 
The fecond effed of elementary fire is dilatation in 
all foiid bodies, and rarefadion i& all fluids. 
Numerous experiments make it evident, that both 
thefe are infeparable from heat. If you heat an iron 
rod, it will increafe in all its dimenfions ; and the 
more it is heated, the farther it will be increafed ; and 
being again expofed to the cold, it will contrad, and 
fucceflively return through all degrees of its dilatation, 
till it arrive at its firft bulk, being never two minutes 
fucceflively of the fame magnitude. 
The like may be obferved in gold, the heavieft of all 
bodies, which takes up more fpace when it is fufed 
than it did before ; nay, even mercury, the heavieft 
of all fluids, has been known to afcend above thirty 
times its height, being placed over the fire in a 
tube. 
The laws of this expanfion are ; 
i ft. That the fame degree of fire rarefies fluids 
fooner, and in a greater degree than it does folids. 
Without this, the thermometer would be of no ufe ; 
fince, if it were otherwife, the cavity of the tube 
would be dilated in the fame proportion as the fluid is 
rarefied. 
2dly, By how much the liquor is lighter, by fo much 
the more it is dilated by fire : thus air, which is the 
lighted: of all fluids, expands the moft, and fpirit of 
wine the next after air. 
The third effed of fire on bodies is motion ; for 
fire, in warming and dilating bodies, muft neceflarily 
move their parts. And in effed, all the motion of 
nature arifes from fire alone ; and if this were taken 
away, all things would become immoveable. AIL 
oils, fats, waters, wines, ales, fpirits of wine, vege- 
tables, animals, &c. become hard, rigid, and inert, 
upon the abfence of only a certain degree of fire ; and 
this induration will be both the fooner, and the more 
violent, "the lefs the degree of fire is. 
Hence, if the fire was abfolutely taken away, and 
there were the greateft degree of cold, all nature 
would grow into one concrete body, foiid as gold, 
and hard as a diamond ; but, upon the application of 
fire, it would recover its former mobility. 
And, of confequence, every diminution of fire is at- 
tended with a proportionable diminution of motion. 
Pure fire is found in two different manners, either 
as it exifts every where, and is diffufed equally in 
all places ; or as it exifts in certain bodies, in which 
it makes no great alteration. 
That fire fhould exift in the fame quantity in all 
places, will feem a ftrange paradox ; and yet that 
it does fo, is demonftrable from innumerable expe- 
riments. 
This elementary fire is prefent every where, in all 
bodies, all fpace, and at all times, and that in equal 
quantities ; for let a perfon go where he will, to the 
top of the higheft mountains, or defcend into the 
loweft cavern, whether the fun fhine or not ; either in 
the moft fcorching fummer, or the fharpeft winter ; 
fire may be colleded by feveral methods, as attrition 
or otherwife. In a word, there is no phyfical point 
aflignable without fire, no place in nature where the 
attrition of two flicks will not render it fenfible. 
The Carteflans, as Marriotte, Perrault, &c. hold. 
That there is a large flock of fire in a perfed vacuum, 
i. e. a fpace out of which all the air has been exhaufted, 
as fuppofing an abfolute vacuum impoflible : now, 
the moft perfed vacuum that we can arrive at, is that 
of Mr. Hugyens’s contrivance, which is as follows : 
heat a quantity of the pureft mercury to the heat of 
boiling water, and pour it into a hot tube of about 
forty inches long ; and when the tube is filled, apply 
a finger upon the orifice of it, and thus invert it into 
a bafon full of mercury : the mercury will now be 
fufpended in the tube to the whole height ; but then, 
if you give it but a little fhake, it will fink down to 
the height of about twenty-nine inches, and thus 
leave a vacuity of eleven inches. 
Yet here the philofophers above-mentioned deny there 
is any vacuum, and urge, that now fo much the more 
fire is entered into the fpace as there was of other 
matter j 
