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the metcor, in the direction of N. E. E. Hence the meteor, at the time when it was higheft at Windfor, muft have been nearly over Sudbury, in Suffolk; and its perpendicular height, above that place, about 36 ftatute miles. Several other obfervations of this meteor have come to my hands, but they are fo inconfiftent with thefe already related, as well as with one another, that I forbear to mention them; and the rather, as they exhibit no circumstances that tend to afcertaining the height or direction of this molt curious and beautiful phenomenon. I fhall, therefore, proceed to lay before my readers the opinions that have been entertained by the moft judicicus philofophers concerning appearances of this kind.

In the 341ft number of the Philofophical Tranfactions for October, November, and December, 1714, Dr. Halley, after relating the circumftances which had been obferved to attend feveral of thefe meteors in various parts of the world, but particularly that mentioned (p. 449) from Montanari, feems to think they must be fome collection of matter, formed in the ether by a fortuitous concourfe of atoms, which the earth meets with in its annual circuit through the ecliptic; and that the great variety of motions which they are found. to have arife from different combinations of the velocity they may have acquired towards the fun at the time when the earth falls in with them, the attraction of the earth's gravitation, and the refiftance they meet with, on approaching our atmofphere.

This hypothefis, like all thofe which have been formed by this most excellent philofopher, is exceedingly ingenious; and I know of no folid objections that can be brought against it, could we but learn how thefe atoms, thus fuppofed to be congregated in the ether, come into, or are generated in it. It is true, indeed, fome years afterward, giving an account of that very remarkable meteor which was feen almost all over England, as well as the neighbouring kingdoms, on the 19th of March 1719, he attempts

to fhew, in fome measure, how this may happen, as follows: "The unufual and continued heats of the laft fummer (fays he) in thefe parts of the world may be fuppofed to have excited an extraordinary quantity of va pour of all forts; of which the aqueous, and most others, being foon condenfed by cold, and wanting a certain degree of fpecific gravity in the air to buoy them up, afcend but to a finall height, and, therefore, are quickly returned in rain, dews, &c. whereas the inflammable fulphurcous vapours, by an innate levity, have a fort of is centrifuga, and not only have no need of the air to fupport them, but being agitated by heat, will afcend in the receiver of an air-pump, and fublime to the top of it, when moft other fumes fall inftantly down, and lie like water at the bottom. From hence we may comprehend how the matter of the meteor might have been raised from a large track of the earth's furface, and afcend far above the reputed limits of the atmosphere; where, being difengaged from all other particles (by a principle in nature that congregates all homogeneous particles, and which is vifible in fo many inftances) its atoms might, in length of time, coalefce and run together, as we fee falts fhoot in water; and gradually contracting themfelves into a narrower compafs, might lie, like a train of gun-powder in the ether, till catching fire by fome internal ferment, as we find the damps in mines frequently do, the flame would be communicated to its continued parts, and run on like a train when fired. This will explain how this meteor came to move with fuch an inconceivable velocity; for if a continued train of powder were no thicker than a barrel, it is not eafy to fay how fast the fire would fly along it; much less can we imagine the rapidity of it along thefe more inflammable vapours, lying in a train of fo vaft a thickness. Suppofing this to be the cafe, it was not a globe of fire that ran along, but a fucceffive kindling of new matter; and as fome parts of the earth might emit thofe this train might in fome parts of it vapours in greater plenty than others,

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be bigger and denfer than in others, which might not only occafion feveral fmaller explofions as the fire went along, but alfo thofe greater ones, which were like the blowing up of large magazines."

Here, though the Doctor has attempted to fhew how thefe vapours may rife above the fenfible limits of our atmosphere, yet it must be obferved that he has changed his opinion greatly with refpect to the manner in which they operate, and the principles on which their motion depends. I fhall not hazard a conjecture concerning the merits or demerits of either opinion; fome objections may undoubtedly be made to both, arifing from difcoveries made by later philofophers; and the Doctor was himself aware of others, which he has endeavoured to obviate.

The late truly worthy, and very ingenious SIR JOHN PRINGLE, P. R. S. after giving all the accounts he could meet with of that remarkable meteor which was feen on the 26th of November 1758, fubjoins fome remarks on meteors of this kind, in which he brings many objections against both thofe hypothefes, and drops hints that imply a perfuafion of thofe bodies being of a much more durable kind than is yet generally fuppofed. For, after fpeaking of the vaft height that meteor was at, the exceeding rarenefs of the atmosphere at that height, the very fmall report which gun-powder, pulvis fulminans, &c. make when fired in an exhausted receiver, and the digious great one which that meteor made when it burft over the city of Glafgow, or thereabout, he adds, "I would infer from hence, that the feparation of the elastic matter muft have been performed with a velocity exceeding all imagination; as the intenfity of found depends fo much on the refiftance of the air, and as this elaftic matter could fly off with fo much celerity, as to find fo great an oppofition from fo thin a medium.

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"I fhould alfo conclude, from the greatnefs of the report, that the fubitance of the meteor was of a firmer

LOND. MAG. Dec. 1783.

texture than could arife from mere exhalations, whether formed into a fphere, and then burning; or difpofed into a kind of train, and confumed by a running fire."

After adding many other arguments against the two hypothefes of Dr. Halley, and alfo to prove that these bodies are not terreftrial exhalations, he concludes his remarks in the following words: "If it is then probable that thefe balls of fire come from regions far beyond the reach of our vapours; if they approach often fo near to our earth, and fo feldom or never touch it; if they are moved with fo much celerity, as in that refpect to have the character of celeftial bodies; if they are feen flying in all directions, and confequently have a motion of their own, independent of that of our globe; if they part with great quantities of elaftic fluid, a phlogistic matter, and probably an acid, furely we are not to confider them as indifferent to us, much lefs as fortuitous maffes, or trains of terreftrial exhalations in the ethereal regions; but rather as bodies of a nobler origin, poffibly revolving about fome centre, formed and regulated by the Creator for wife and beneficent purposes, even with regard to our atmofphere; which, during their combuftion, they may fupply with fome fubtile and falutary matter, or remove from it fuch parts as begin to be fuperfluous, or noxious to the inhabitants of the earth."

Some may perhaps be as little fatisfied with the opinion of this learned and good man as with those of Dr. Halley: I, for my part, am equally difinclined to comment on either; but having laid before my readers the whole stock of our knowledge on this fubject, both in fact and theory, recommend to every one of them to add to it whatever may be in their power, by obferving and recording, in fome publication or other, fuch circumtances attending future meteors of this kind, as will tend to explain their na ture and properties, as well as afcertain their fituation and motions.

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TO THE READERS OF THE LONDON MAGAZINE.

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E have been favoured with the following paper from Dr. Mafkelyne tions and ingenious remarks of fo able an aftronomer. This paper will ferve as an appendix to the full account of the Fire-Balls, which precedes it, and cannot but attract the notice and attention of our readers in a high degree, both from the nature of the subject, and from the able manner in which it is treated. It is no eafy task to unite entertainment with philosophy.

PLAN FOR OBSERVING THE METEORS CALLED FIRE-BALLS, BY NEVIL MASKELINE, D. D. F. R. S. AND ASTRONOMER ROYAL.

altitude, compared with that of the fun or moon at the fame altitude; the brightnefs and colours of its light, and the degree of illumination which it gave; and to make a sketch or drawing of the appearances before and after it burft, or any other of its appearances.

4th. Whether both the body and the tail burft; and how many parts this burfting produced; and whether this happened before or after it arrived at its greateft apparent altitude; the length of the tail before the meteor burst; and indeed every alteration of its length they obferve; whether the meteor appeared very faint at firft, and gradually grew brighter, or appeared very bright at once; and whether it was extinguished fuddenly, or by degrees.

FIVE IVE meteors, of the kind which from their appearance are generally called Fire-balls, have been feen of late, in the space of a few weeks, viz. on August 18th, Sept. 26th, October 4th, 19th, and 29th, which feems to indicate that they appear more frequently than is commonly imagined. The curious and extraordinary appear ances which they exhibited, fhew them to be deferving more attention than has been hitherto given them. For want of a feries of proper obfervations, little progrefs has been made towards accounting for their phenomena. The greater part of thofe who have feen them, not being previously acquainted with the circumstances they ought to attend to, have made obfervations too imperfect to answer that purpofe. It is, therefore, to be wifhed that all perfons who may happen to fee a meteor would attend to the following particulars, and fet down their remarks as foon as they can after they fee it, while the impreffion made by the me- 7th. The bearing and distance of the teor is full and fresh in their memory, place of obfervation from the nearest before it is vitiated by their own after-market-town fhould be put down. thoughts, or the accounts received from other obfervers. Such after-thoughts may be of great ufe: but their own genuine original obfervations are chiefly to be wished for by any one who is to calculate the track of the meteor.

The particulars to be attended to are thefe.

ift. The precife time of its appearance. zd. Its apparent altitudes and bearings at its first appearance, at its greateft elevation, at its buriting, and at its difappearance..

3d. Its figure, and the diameter of the body when at the greatest apparent

sth. How long the appearance lafted. 6th. Whether a found or founds (as of an explosion) was heard fome minutes after its difappearance, and how long, and from what point of the pafs they thought it came.

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N. B. As found moves only at the rate of 13 miles in a minute, the obferver fhould patiently wait for at leaft 8 or 10 minutes, liftening for the found, for all meteors appear to be very many miles indeed nearer to the obferver than they really are.

REMARK S.

Curious perfons may avail themfelves of obfervations made even by the most illiterate, by caufing them to trace with a tick the path which the meteor defcribed in the Heavens, according to the beft of their recollection. The obfervations would be better made,

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if you accompany the perfon to the very fpot where he faw the meteor, for there the neighbouring objects, fuch as roads, houfes, or trees, will much affift his memory.

The apparent altitudes of the meteor are best found by a quadrant (a common wooden one of three inches radius divided into degrees will fuffice) which the perfon should direct to the points in the Heavens where the meteor appeared to him, if he faw it, or even to fuch points where the illiterate perfon abovementioned pointed. In like manner its bearings fhould be found by a compafs.

To afcertain how long the appearance lafted, he should trace over its path in the Heavens with its proper velocity, while another perfon obferves the time by a watch or clock that fhews feconds; or by the number of fwings of a temporary pendulum made by a mufket ball, or any fmall weight fufpended by a ftring of 39 inches long from the centre of the ball or weight, which will fwing feconds. Without fome fuch method as this, they will be apt to eltimate the time much longer than it is.

It would be well if thofe perfons, who happen to fee a meteor, would put down the time by their watch when it first appeared, or was at its greateft altitude, or burft, or difappeared, and again when they hear the found; and, as common watches are liable to vary much in a few hours, that they would, as foon after as may be, find the error of their watch by comparing it with a good regulator; for, if the exact times could be had at different places, the

SIR,

As

abfolute velocity of the meteor, the velocity of the found propagated to us from the higher regions of the atmofphere, and the longitudes of places might be determined.

Even in cloudy weather it might be ufeful to note the times of accidental explofions, or any unufual founds heard, with the points of the compafs from which they are thought to come, whether in the day or night, and of fudden illuminations of the fky in the night, as they may prove afterwards to have been owing to meteors, and will ferve fome of the purpofes abovementioned.

Thefe meteors generally leave a vifible tract of faint light behind them, which gives time to obfervers to afcertain the path, either by the ftars near it, or the obfervations of altitudes and bearings. Meteors are fometimes feen

in the day-light.

It may not be amifs to apprize obfervers, that cftimations of altitudes made without an inftrument are very uncertain, owing to the apparent figure of the fky being the fegment of a fphere, whofe centre is greatly below the furface of the earth; fo that perfons will be apt to judge an object which is near the horizon to be much higher than it is; at 23° of altitude, they may think it at 45°; and to be in or near the zenith, when with an inftrument it would be found 10 or 20 degrees from it. This points out the neceffity for obfervers to mention, whether they eftimated their altitudes, or obferved them with an inftrument.

Greenwich, November 6th 1783.

TO THE EDITOR OF THE LONDON MAGAZINE.

S the aeroftatical experiments lately made in France and in London have juftly engaged the attention of the public, I am willing to imagine that an account of the principle upon which they are performed will be acceptable to the readers of your ufetul and entertaining mifcellany. If your opinion coincides with mine, I fhall be glad to fee the following pages inferted."

N.

MONG other diftinctions by fluidity is one of the moft remarkable. it is a body whofe parts yield to any 352

that which refpects their folidity or

force

force impreffed upon them, and in yielding are cafily moved amongit each other. From this effential property of a fluid it happens that any preffure whatfoever which is made upon any part is communicated in all directions to the reft, and even that preffure which arifes from the gravity or weight of the parts of any fluid is made to act in the fame manner. So that if any fubftance be immerfed, for example, in water, its upper part will be preffed by, or sustain the weight of all the water which lies perpendicularly above it, and this preffure will therefore be in proportion to its depth beneath the furface: and again, becaufe any lower part of the fluid is preffed by the weight of the upper parts, from which, by its own nature as a fluid, it will endeavour to recede in every direction, the parts beneath the fubftance immerfed will likewife prefs upwards in a like proportion. But the preffure beneath will exceed the preffure above in the proportion of the difference between the depths of the under and upper furfaces. That is to fay, all circumftances being confidered, any body whatsoever immerfed in a fluid will be preffed upwards by a force which is equal to the weight of a mafs of the fluid equal in bulk to the body immerfed. This very ufeful hydroftatical theorem is applicable to the mat

ter before us.

For it is clear, that if the whole weight of the body immerfed be not equal to a mafs of the fluid of the fame magnitude, the upward preflure will exceed the gravity of the body, and confequently it will afcend to the furface. This is the caufe why fome bodies fwim, and the converfe of this reafoning fhews why others fink.

We are not at all furprifed to fee bodies fwim in water, becaufe we are familiarized to experiments with this denfe fluid. The vulgar behold facts, and reft contented, without farther enquiry. Eut the philofopher purfues diftant analogies, and forms remote combinations, in the extended arrangements that occupy his attention, which the lefs thoughtful part of mankind

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often deride, as the vifionary offspring of a deluded brain. Sir Francis Ba con was one of the first philofophers who made it an object of enquiry, whether bodies might not be constructed fo light as actually to become buoyant or float in air; and the enquiry has been renewed fince the more perfect difcovery of the air-pump, and the weight of the atmosphere. The refult of this was, that the attempt by means of exhaufting the internal air is in its own nature incapable of being attended with fuccefs. For an hollow metallic fphere, of ftrength fufficient to support the external preflure of the atmosphere when the internal air is exhausted, will in all cafes be heavier than an equal bulk of air, and, therefore, will not afcend. The archives of the Royal Society contain the firft, and perhaps the only attempt to float bodies in condenfed air. This is mentioned in Spratt's Hiftory of the Royal Society, p. 218, in a manner which does not clearly determine whether it was attended with fuccefs or not.

It has already been laid before the public* what were the preliminary difcoveries among the English, which led their neighbours and rivals, the French, to that fuccefsful experiment which future ages will mention to their honour. Happy would it be for both nations, if we might indulge the Utopian with that all other rivalry between them might ceafe, except that of mutually ftriving to go beyond each other in promoting thofe fciences on which the welfare of fociety depends! Let us throw away the mean and interefted ambition which prompts us to decry the merit of men who happen not to have been born in our island; and while we enjoy the produce of their induftry and abilities let us allow them their fhare of fame. England can boast of Newton, who is with juftice called the first of men; but if France had never produced Defcartes, the great and immortal Sir Ifaac would perhaps have been no more than the firft fcholaftic fophifter of his time.

The atmosphere or body of air which environs the globe is compofed of parts September laft, p. 281.

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