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after the end of this year, from the anfwers to the prize queftion propofed by the Royal Academy of Sciences at Paris, to compute the disturbances of the comet of 1532 and 1661, and thence to predict its


"If it fhould come to its perihelium on the 1ft of January 1789, it might probably be vifible, with a good acromatic telescope, in its defcent to the fun, the middle of September 1788, and fooner or later according as its perihelium hould be fooner or later. It will approach us from the fouthern parts of its orbit, and therefore will first appear with confiderable fouth latitude and fouth declination; fo that perfons refiding nearer the equator than we do, or in fouth latitude, will have an opportunity of difcovering it before us. It is to be wished that it may be first feen by fome aftronomer in fuch a fituation, and furnished with proper inftruments for fettling its place in the heavens, the earliest good obfervations being most valuable for determining its elliptic orbit, and proving its identity with the comets of 1532 and 1651. The Cape of Good Hope would be an excellent fituation for this purpofe.

"In order to affist aftronomers in looking out for this comet, I have here given its heliocentric

and geocentric longitudes and latitudes and correfpondent distances from the fun and earth, on fuppofition that it fhall come to its perihelium on January 1ft, 1789. But if that should happen fooner or later, the heliocentric longitudes and latitudes and diftances from the fun will stand good, if applied to days, as much earlier or later as the time of the perihelium may happen fooner or later; and the geocentric longitudes and latitudes and diftances from the earth must be recomputed accordingly. The calculations are made for a parabolic orbit from the clements determined by Dr. Halley from Hevelius's obfervations in 1651, only allowing for the preceffion of the equinoxes. The elements made ufe of were as follows:

Time of perihelium January 1, 1789, at noon.

Perihelium diftance, 0,44851.
Place of afcending node 2 24


Inclination of orbit to the ecliptic 32° 36′.

Perihelium forwarder in orbit than the afcending node 33° 28'. Its motion is direct.

In the following table are fet down the computed places of the comet, on fuppofition that it fhall return to its perihelium January 1, 1789, at noon.

4,52 11
2,57 11 11 16
2,15 11 13 47


|Dift | Dist. (Heliocen- Helio- | Geocen- Geocen- |Product of
from from tric lon-centric tric lon- tric distances
gitude. latitude. gitude, latitude. from

Apr. 23, 74,0
June 4, 13, 5
July 14, 53,
Aug. 2,46 2,75

and earth.

5. D. M. D. M.
3 54 30 56S

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7 6 31 25
31 55

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32 22

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of 48


932 32

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1,29 11 24 16 32 36
1,13 11 29 24
1,01 O 5 51

11-13 12 56 45


32 30

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Nov. 9,34 1,25

0,88 O 14 19 31 о
23,391,0 0,760 26 4
Dec. 7,210,75 0,62 1 13 58
23,320,50 0,50 2 20 58
24,35 0,49 0,51

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8 36 46 47


28 32

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1, 0,45 0,50

2 24 18 Jan. 3 23 25 "The last observation made by Hevelius on the comet in 1661 was when its distance from the earth was 0,986, and from the fun 1,37, with what he calls a very long and good telescope; at which time it appeared faint and fmall with it, though ftill fufficiently vifible. Let us fuppofe this to have been a telefcope of 9 feet focal length, with an aperture of 1,65 inch; then, becaufe the diameter of the aperture of a telescope fufficient to render

17 17N 9 2 50 13 8N 0,26
the comet equally vifible should be
as the product of its diftances from
the fun and earth, and the product
of the numbers above mentioned
0,986 and 1,37 is 1,35, we shall
have the following analogy to fird
the aperture of a refracting tele-
fcope fufficient to show the comet
as it appeared to Hevelius. As
1,35 1,65 inch :: 9: 11 inches,
fo is the product of diftances from


the fun and earth to the diameter of the aperture required in inches."


"1. THE kind of matter which

impreffes us with a fenfe of beat, and which is capable of expanding and pervading all known bodies, is fubject to larvs of attraction, which fixes and difguifes a certain quantity of it in divers fubftances; and this matter produces the effects which ave call heat, and acts as fire, only when it is extricated from other kinds of

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ceffes are the mixtures producing heat, the abforptions of divers cold elastic fluids cauting heat, vitriolizations, incalafcence of pyrophori, refpiration, putrefaction, fermentation, and combuftion. In all these, the matter of fire, fo foon as it is liberated, is found by its peculiar effects, and the menfurable decrease of heat at increased distances from the fource of emiffion, to move excentrically from that fource, and to decrease in denfity. But as this happens, whether the extrication of it be attended with illumination or not, it indicates nothing that is confiftent with the tenor of nature, or that may be fuggefted by analogy, except that the parts of the matter of fire repel each other, although they certainly are attracted by other kinds of matter. This repellant property is equally apparent in every inftance of the formation of elastic fluids from aggregate bodies; and especially when this is done by mere ignition. But as thefe inftances afford another inference of equal ufe, I fhall fubjoin them to the following notion.

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3. The matter of fire, by virtue of the repulfion fubfifting between its homogeneal parts, and of their attrac tions to the parts of other matter, is the caufe of the elafticity of aeriform fluids.

"This notion is neceffary to the folution of the phenomena, and is fupported by direct evidence, of which the following part will be fufficient.

"Oils, refins, vegetable acids, charcoal, and divers other bodies, are almost totally convertible into fixable air and inflammable air by fire. Nitrous acid may be decompofed and converted, in part, into empyreal air, in the remainder into phlogistic or nitrous air, by the agency of fire. The whole fubitance

of folid nitrous ammoniac is convertible into fluids permanently elaftic, by the mere action of fire. From the folid aggregation in manganefe and other metallic calxes, and in divers falts, the grofs matter of empyreal air may be propelled, to form an elaftic uid by fire; fo may that of dense inflammable air from coak and divers hard bodies; that of fixable air from itony concretes; that of alkaline air from ivory, Pruffian blue, and microcofmic falt; that of vitriolic, or of marine, or of hepatic air, from divers folid, faline, or fulphureous compounds. All this is done by fire; and being beft effected in veffels that are impervious to every other known matter, amounts to a fatisfactory proof that the matter of fire is the only acceffary and agent in the conversion of solid bodies into elastic fluids, and in the maintenance of their elasticity.

"The electric matter is not to be mentioned in objection, until it is proved that it does not itself confit of the matter of fire, in a certain modification of it, depending on the repulfive property, and the relations to grofs matter, which we are now defcribing.


"Seeing this extensive agency the fiery matter; that we can not only trace it into the fubjects which thus become permanently elaftic, but that it gives a temporary elasticity to vapours and fublimates ; feeing that thefe refume their ag them; that its union in the fluids, gregation as faft as it escapes from to which it gives permanent elafticity, may be further proved by the extrication of it from every one of them; and that, in thefe liberations of it which are daily experienced, in the abforptions of elastic fluids, in combinations, and in combuftions of them, the emiffion

is fo copious as to remove all doubt of their having held it in great quantity, united with their relpective feparated parts, and reftrained during that union from acting like liberated fire; obferving alfo, that as fast as the fire is liberated or excluded, the diftant groffer parts of elastic fluids rufh together or into other bodies; as when empyreal and nitrous air makes nitrous acid, or empyreal and light inflammable air make water which cools to folid ice, or marine and alkaline air make fal ammmoniac; or as when acid or alkaline airs rufh into water, or empyreal air into phosphorus; we cannot now helitate in admitting that the groffer parts of elaftic fluids, as well as thofe of vapour, are made to recede from each other contrary to their inherent and inceffant attractive powers, by virtue of their respective charges of the repellent matter of fire, and confequently by the repulfion of the parts of fire to each other.

"4. The charges of repellent matter, by which attractive and gravitating particles form elaftic fluids, are diftinct atmospheres of fiery mat ter, in which the denfities are reciprocally as the diftances from the central particles, in a duplicate or higher


"This is an evident confequence of the former notions, and the prevalence of the repulfive over the attractive forces; and the terreftrial atmosphere, in which the denfity is inverfely as the fquares of the diftances from the earth, fhews that it is the natural and neceffary effect of fuch forces, to form the charges of fiery matter which the particles engage, into the defcribed atmospheres. The further evidence of the truth of this notion arifes from phenomena, which I am prefently to confider and ex

plain, and which are not inexpli cable by any other condition or agency of the matter of fire, that has been hitherto fugge led.

"5. The repulfion of the homoge neal parts of the matter of fire, limits the quantity that can be engaged by bodies, and tends to diffuse the remainder equably in fpace.

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"This notion needs no illuftration. "6. The matter of fire limits the quantities, in which aeriform fluids, and bodies containing it, can combine chemically.

"In the converfion of folid bodies into elastic fluids, we perceive the repulfive forces of the matter of fire refifting and overpowering the reciprocal attractions of the groffer parts; and in mixtures of empyreal and inflammable air, and in divers other mixed airs, we fee this matter refifting the attractions which tend frongly to the chemical combination of the heterogeneal gravitating particles.

"In fuch inftances it is manifest that the fum of the repulfive forces, exceeds that of the attractive.

"When aeriform fluids condenfe each other, or are concentrated and aggregated by bodies, it is equally evident that the attractive forces, although refifted by the repulfive, are prevalent.

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Thefe, and divers other phenomena fhew, that the natural power, whether attractive or repul five, of each part of matter, is limitted; and therefore the sum of thefe powers which any body can exert in regard to another, is by a law of nature as the number of its active parts, or in other words, as its quantity of matter.

"In confequence of this law, the fum of the repulfive forces, which refift the approximation of the gravitating parts of an elaftic fluid, and their union with those of a bo


dy which alfo holds fome of the matter of fire, is as the quantity of that fluid; and no more than a determinate portion of it can be aggregated and combined in the body whole quantity of matter and at tractive powers are limited.

"By the fame law it is determined that elaftic fluids fhall unite with each other in limited proportions only, to form denfer fluids or folid bodies, and that the fuperfluous quantities fhall remain elattic and unaltered.

"As the matter of fire is manifeftly the agent which refifts the coalefcence and union of attractive particles in thefe cafes; and as the fame matter demonftrably exifts in all bodies that unite only in limited proportions, we muft afcribe to this only competent and manifest agent, all thofe limitations which we experi ence, in regard to the proportions in which bodies can be chemically united, and which we briefly exprefs by the word faturation.



[From the fame Work.]

S the limits of this effay do not permit me to make extentive applications of the foregoing notion, I fhall endeavour, in the expreffion of a few, in this and the following fection to fuggeft e. very thing that feems neceffary towards explaining the most intricate phenomena of the matter of fire.

"In regard to the apyrous bodies, fuch as the pure earthy fubtances, I would infer from thefe notions that they chiefly confift of parts which do not attract the matter of fire with forces fufficient to caufe a difunion of them, and an interpofition of this matter in fuch quantity as to induce foftnefs or fluidity.

"Concerning fufible bodies which concrete in cooling, I would in the next place infer, that they confift chiefly of parts which attract the matter of fire with forces fomewhat greater than thofe laft men ioned, and fuffic ent to effect the folution of them in the fiery fluid, but not for the permanent retention of it: That bodies of this clafs exclude the folvent by virtue of the preva1786.

lent attractions which tend to reunite their grofs parts; but that they receive and tranfmit the matter which caufes heat, more freely, and they retain it longer, than the former can in fimilar circumftances, by reafon of the ftronger attractions.

"The bodies, which, like oils or water, form elaflic vapour, when duly charged with the matter of fire, confift chiefly of parts which attract it with forces fill greater, and fufficient to compel atmospheres around the diftant molecules; but yet not fufficient to retain thefe atmofpheres after the influx of fire ceafes, and in oppofition to the mutual attractions of their central molecules, and the tendency of the fiery matter to diffufe itself equably in the neighbouring spaces. As the thermometer fhews no more than the relative quantities of free matter of fire in bodies, thefe lately mentioned require a greater quan tity of the fiery matter than the former, before they exhibit an equal temperature by the thermome ter, for the reafon already men tioned.

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