Balls of FIRE

Balls of FIRE, in meteorology, a kind of luminous bodies generally appearing at a great height above the earth, with a splendor surpassing that of the moon; and sometimes equalling her apparent size. They generally proceed in this hemisphere from north to south with vast velocity, frequently breaking into several smaller ones, sometimes vanishing with a report, sometimes not.

These luminous appearances no doubt constitute one part of the ancient prodigies, blazing stars or comets, which

which last they sometimes resemble in being attended with a train; but frequently they appear with a round and well defined disk. The first of these of which we have any accurate account, was observed by Dr Halley and some other philosophers at different places, in the year 1719. From the flight observations they could take of its course among the stars, the perpendicular height of this body was computed at about 70 miles from the surface of the earth. The height of others has also been computed, and found to be various; though in general it is supposed to be beyond the limits assigned to our atmosphere, or where it loses its refractive power. The most remarkable of these on record appeared on the 18th of August 1783, about nine o'clock in the evening. It was seen to the northward of Shetland, and took a southerly direction for an immense space, being observed as far as the southern provinces of France, and one account says that it was seen at Rome also. During its course it appears frequently to have changed its shape; sometimes appearing in the form of one ball, sometimes of two or more; sometimes with a train, sometimes without one. It passed over Edinburgh nearly in the zenith, and had then the appearance of a well defined round body, extremely luminous, and of a greenish colour; the light which it diffused on the ground giving likewise a greenish cast to objects. After passing the zenith it was attended by a train of considerable length, which continually augmenting, at last obliterated the head entirely; so that it looked like a wedge, flying with the obtuse end foremost. The motion was not apparently swift, by reason of its great height; though in reality it must have moved with great rapidity, on account of the vast space it travelled over in a short time. In other places its appearance was very different. At Greenwich we are told, that "two bright balls parallel to each other led the way, the diameter of which appeared to be about two feet; and were followed by an expulsion of eight others, not elliptical, seeming gradually to mutilate, for the last was small. Between each two balls a luminous serrated body extended, and at the last a blaze issued which terminated in a point. Minute particles dilated from the whole. The balls were tinted first by a pure bright light, then followed a tender yellow, mixed with azure, red, green, &c.; which, with a coalition of bolder tints, and a reflection from the other balls, gave the most beautiful rotundity and variation of colours that the human eye could be charmed with. The sudden illumination of the atmosphere, and the form and singular transition of this bright luminary, tended much to make it awful: nevertheless the amazing vivid appearance of the different balls, and other rich connective parts not very easy to delineate, gave an effect equal to the rainbow in the full zenith of its glory."

Dr Blagden, in a paper on this subject in the 74th volume of the Philosophical Transactions, has not only given a particular account of this and other meteors of the kind, but added several conjectures relating to the probable causes of them. The first thing which occurred to philosophers on this subject was, that the meteors in question were burning bodies rising from the surface of the earth, and flying along the atmosphere with great rapidity. But this hypothesis was soon abandoned, on considering that there was no power known by which such bodies could either be

raised to a sufficient height, or projected with the velocity of the meteors. The next hypothesis was, that they do not consist of one single body, but of a train of sulphureous vapours, extending a vast way through the atmosphere, and being kindled at one end, display the luminous appearances in question by the fire running from one end of the train to the other. To this hypothesis, which was invented by Dr Halley, Dr Blagden objects that no just explanation is given of the nature of the vapours themselves, the manner in which they are raised up, or in which they can be regularly arranged in straight lines of such vast extent; or how they can be supposed to burn in such rarefied air. "Indeed," (says he) it is very difficult to conceive how vapours could be prevented, in those regions where there is in a manner no pressure, from spreading out on all sides in consequence of their natural elasticity, and instantly losing that degree of density which seems necessary for inflammation. Besides, it is to be expected, that such trains would sometimes take fire in the middle, and thus present the phenomenon of two meteors at the same time, receding from one another in a direct line."

For these and other reasons this hypothesis of Dr Halley was abandoned, and another substituted in its place. This was, that the meteors we speak of are permanent solid bodies, not rising from the earth, but revolving round it in very eccentric orbits, and thus in their perigee moving with inconceivable rapidity. But the Doctor shows, that even on this supposition, the velocity of such bodies must scarce be one third of that with which fire-balls move, and which has been calculated at upwards of 1000 miles per minute. The hypothesis is likewise liable to a number of other objections which cannot be answered, particularly from the variations in their appearance; for it is impossible to show in what manner one solid and permanent body could assume the appearance of eight or ten, as was the case with the meteor of 1783; nor can it be shown why a body, which in passing over Edinburgh appeared with a disk evidently less than that of the sun, should, in passing over Greenwich, assume the appearance of two bodies, each of which had a disk considerably larger than the apparent disk of that luminary. To obviate, in some measure, objections of this kind, it has been supposed that the revolving bodies are surrounded by a kind of electrical atmosphere by which they are rendered luminous; "but (says the Doctor) I think, whoever carefully peruses the various accounts of fire-balls, and especially ours of the 18th of August, when it divided, will perceive that their phenomena do not correspond with the idea of a solid nucleus involved in a subtle fluid, any more than with the idea of another learned gentleman, that they become luminous by means of a contained fluid, which occasionally explodes through the thick solid outer shell."

Another hypothesis, which Dr Blagden has not mentioned, is, that the meteors in question are a kind of bodies which take fire as soon as they come within the atmosphere of the earth. But this cannot be supposed without implying a previous knowledge of these bodies, which it is altogether impossible we can have. The only opportunity we have of seeing them is when they are on fire. Before that time they are in an invisible and unknown state; and it is surely improper to ar-

gue concerning them in this state, or pretend to determine any one of their properties, when we have it not in our power to see or investigate them in the least. As the meteors therefore never manifest themselves to our senses but when they are on fire, the only rational conclusion we can draw from thence is, that they have no existence in any other state; and consequently that their substance must be composed of that fluid which, when acting after a certain manner, becomes luminous and shows itself as fire; remaining invisible and eluding our researches in every other case. On this hypothesis we must conclude that the fire-balls are great bodies of electric matter, moving from one part of the heavens where, to our conception, it is superabundant, to another where it is deficient. This opinion is adopted by Dr Blagden for the following reasons:

1. On account of their prodigious velocity, which is not less than 1200 miles in a minute, and seems incompatible with any other substance we know besides the electric fluid. "This (says he) is perhaps the only case in which the course or direction of that fluid is rendered perceptible to our senses, in consequence of the large scale on which these meteors move."

2. Various electrical phenomena have been observed to attend them, such as lambent fires settling upon men, horses, &c. and sparks coming from them, "or the whole meteor itself (adds our author), it is said, have damaged ships, houses, &c. after the manner of lightning." This last circumstance, however, we can believe only of another kind of fire-balls, of which we shall afterwards treat, which keep at a small distance from the earth, or run along its surface; for the great meteors of which we now speak, flying at the distance of 50 or 60, or more miles from the surface of the earth, cannot be less from their apparent size than a mile or a mile and an half in diameter. Such an immense body of electric matter descending on the earth, would by its explosion ruin a large tract of country; and there is no probability that when engendered in such a rare atmosphere it could break through the whole body of gross and dense air which lies between these regions and the earth, and which we know resists the passage of the electric fluid very strongly. Notwithstanding this, there is no impossibility that the atmosphere may be electrified to a great degree by such a meteor passing over it; and thus electrical appearances may attend these bodies without any actual emission of their substance, as Dr Blagden supposes. "If there be really (says he) any hissing noise heard while the meteors are passing, it seems explicable on no other supposition than that of streams of electric matter issuing from them, and reaching the earth with a velocity equal to that of the meteor, namely, in two or three seconds. Accordingly, in one of our late meteors, the hissing was compared to that of electricity issuing from a conductor. The sparks flying off so perpetually from the body of fire-balls may possibly have

some connection with these streams. In the same manner the found of explosions may perhaps be brought to us quicker than if it were propagated to us by the air alone. Should these ideas be well founded, the change of direction, which meteors seem at times to undergo, may possibly be influenced by the state of the surface of the earth over which they are passing, and to which the streams are supposed to reach. A similar cause may occasion the apparent explosion, the opening of more channels giving new vent and motion to the electric fluid. May not the deviation and explosion which appear to have taken place in the fire-ball of the 18th of August over Lincolnshire, have been determined by its approach towards the fens, and an attraction produced by that large body of moisture?"

The explosion mentioned by our author over Lincolnshire does not seem to have been the only one which happened during the course of this meteor. Several people heard reports after it had vanished; and these were sometimes single and sometimes double. At Edinburgh two reports were heard, the one immediately following the other, at the distance of six or seven minutes after the meteor had passed. These reports no doubt indicated a temporary dissolution of the body; but it is by no means probable that the dissolution could have taken place either on account of the state of the earth or atmosphere. We must consider that both earth and atmosphere are always full of electric fluid; and if there happens to be what is called a deficiency (A) in one of them, the other instantly supplies it. It is impossible, therefore, that either the earth or atmosphere could receive such an immense additional quantity in one part without a vent being provided for it somewhere else. In thunderstorms we naturally conclude that vast quantity of electrical matter is put in motion; but from the effects of lightning it appears that this quantity must be very trifling in comparison with what the meteor we now speak of contained. A violent flash of lightning has been known to perforate a looking-glass, and make only a hole of about an inch diameter. Now we have no reason to suppose that the flash, tremendous as it might appear to our eyes, was any other than an electric spark of an inch in diameter. The meteor, on the other hand, appears not to have been less than a mile in diameter; so that the disproportion betwixt it and a single flash of lightning appears almost beyond calculation; and we may reasonably conclude that it could not have been equalled by 10,000 thunderstorms. Had this amazing body of electric fire descended through the atmosphere and dissipated itself on the fens of Lincolnshire, it must have produced the most violent and unheard of effects, not only in that place, but probably throughout the whole island. Its dissipation must therefore have been in the higher regions, where there was ample space to receive it; and where its explosion, whatever concussion it might make among the ethereal matter itself, could not affect our earth or atmosphere in any remarkable.

markable degree. Its re-appearance was owing to the same tendency in the fluid to circulate which had originally produced it; and which probably was the violent earthquake in Calabria and the eruption in Iceland. See EARTHQUAKE, n° 111.

3. Another argument adduced by Dr Blagden in favour of the electrical origin of fire-balls, is their connection with the aurora borealis, and the resemblance they bear to these phenomena, which are now almost universally allowed to be electrical. "Instances (says he) are recorded, where northern lights have been seen to join, and form luminous balls, darting about with great velocity, and even leaving a train behind them like the common fire-balls. This train I take to be nothing else but the rarefied air left in such an electrified state as to be luminous; and some streams of the northern lights are very much like it." The aurora borealis appears to occupy as high, if not a higher region above the surface of the earth, as may be judged from the very distant countries to which it has been visible at the same time: indeed the great accumulation of electric matter seems to lie beyond the verge of our atmosphere, as estimated by the cessation of twilight. Also with the northern lights a hissing noise is said to be heard in some very cold climates: Gmelin speaks of it in the most pointed terms, as frequent and very loud in the north-eastern parts of Siberia *; and other travellers have related similar facts.

4. Our author thinks that the strongest argument for the electrical origin of these meteors is the direction of their course, which is constantly either from the north or north-west quarter of the heavens, or towards it; or, as our author thinks, nearly in the direction of the magnetic meridian. Such a course, however, seems only to belong to the very large fire-balls of which we now speak; the smaller ones, called Falling Stars, being moved in all directions; "perhaps (says the Doctor), because they come further within the verge of our atmosphere, and are thereby exposed to the action of extraneous causes. That the smaller sort of meteors, such as shooting stars, are really lower down in the atmosphere, is rendered very probable by their swifter apparent motion: perhaps it is this very circumstance which occasions them to be smaller, the electric fluid being more divided in more resisting air. But as those masses of electric matter which move where there is scarce any resistance, so generally affect the direction of the magnetic meridian, the ideas which have been entertained of some analogy between these two obscure powers of nature seem not altogether without foundation. If the foregoing conjectures be just, distinct regions are allotted to the electrical phenomena of our atmosphere. Here below we have thunder and lightning, from the unequal distribution of the electric fluid among the clouds; in the loftier regions, whither the clouds never reach, we have the various gradations of falling stars; till, beyond the limits of our corpuscular atmosphere, the fluid is put into motion in sufficient masses, to hold a determined course, and exhibit the different appearances of what we call fire-balls; and probably at a still greater elevation above the earth, the electricity accumulates in a lighter and less condensed form, to produce the wonderfully diversified streams and coruscations of the aurora borealis."

The paper from whence these extracts are taken was written before Mr Morgan's account of the non-conducting power of a perfect vacuum made its appearance. An abstract of his arguments on this subject is given under the article ELECTRICITY, n° 130-137, and their insufficiency to prove the point intended, is shown under the same article, n° 277. Under that article, we have only mentioned the deficiency in Mr Morgan's argument, without adducing any positive proof to the contrary. Such a proof, however, is offered by the meteor in question, or by others of the same nature. Dr Halley, speaking of the fire-ball of 1719, the height of which he calculated at very little less than 70 miles, expresses his surprise that found should be propagated through a medium near 300,000 times rarer than the common air, and the next thing to a perfect vacuum. Now it remains, and for ever will remain, to be proved, that Mr Morgan's most perfect vacuum, formed by boiling quicksilver in a tube ever so long, contains a medium more than 300,000 times rarer than the common atmosphere.

From Mr Cavallo's experiments * it appears, that when air is only rarefied 1000 times, the electric light is excessively weak; so that there is not the least probability that in an aerial medium 300,000 times rarer than the present, if indeed such a medium can exist, there could be any light made visible in the ordinary experiments. We see, however, by the many examples of meteors which have occurred at prodigious heights in the atmosphere, that the electric light in such a rarefied atmosphere is not only visible, but acts as vigorously in every respect as if it were on the surface of the earth. This circumstance therefore affords a complete demonstration of the fallacy of Mr Morgan's argument, and a direct proof that the electric fluid pervades space as completely divested of air as the best artificial vacuum we can make; nay, where it is generally believed by mathematicians that the atmosphere has ceased altogether. His other arguments drawn a priori are still more inconclusive than that we have just mentioned. He tells us, that if a vacuum was a conductor, the whole quantity of electric matter contained in the earth and atmosphere would be perpetually flying off through the regions of infinite space, as being surrounded by a boundless conductor. But even this does not follow, though we should suppose these regions to be an absolute vacancy; for we know that electricity does not fly to a conducting substance merely because it is a conductor, but because it opens a passage to some place whither it has a tendency to go though the conductor was not there. Now, on the present hypothesis, as the conductor would lead to no place to which the electric matter had any previous tendency, we cannot assign any reason why it should acquire a tendency to fly off merely on account of the neighbourhood of a conductor, even though boundless. His other objection (that, on the supposition of a vacuum being capable of conducting electricity, the whole space in the universe would be filled with electric fluid) may be admitted in its fullest extent, without any detriment whatever to science: and indeed, if we allow the electric fluid to be only a modification of the light of the sun, as is rendered very probable under the article ELECTRICITY, sect. vi. as well as that of FIRE, and many others in various places of this

work, we must own that the whole universe is filled with it. The meteors in question then will be no other than discharges of electricity from one part of the celestial spaces to another, similar to the discharges between the positive and negative side of an electrified bottle; thus intimating, that a circulation has taken place in the fluid, which the meteor at once completes and puts an end to. See the article Meteorology.

Besides these already just mentioned of such vast magnitude, there are others much smaller and nearer the surface of the earth, rolling upon it, or falling upon it, exploding with violence, as is the case with those which appear in the time of thunder, and frequently produce mischievous effects. One of these is mentioned by some authors as falling in a serene evening in the island of Jamaica; exploding as soon as it touched the surface of the ground, and making a considerable hole in it. Another is mentioned by Dr. Priestley as rolling along the surface of the sea, then rising and striking the top-mast of a man of war, exploding, and damaging the ship. In like manner we hear of an electrified cloud at Java in the East Indies; whence, without any thunder storm, there issued a vast number of fire-balls, which did incredible mischief. This last phenomenon points out to us the true origin of balls of this kind, viz. an excessive accumulation of electricity in one part, or a violent tendency to circulate, when at the same time the place where the motion begins is at so great a distance, or meets with other obstacles of such a nature, that it cannot easily get thither. Urged on, however, by the vehement pressure from behind, it is forced to leave its place; but being equally unable to displace the great quantity of the same fluid, which has no inclination to move the same way with itself, it is collected into balls, which run hither and thither, according as they meet with conductors capable of leading them, into some part of the circle. This is even confirmed by an experiment related at the end of Dr. Priestley's fifth volume on Air. He relates, that a gentleman having charged, with a very powerful machine, a jar, which had the wire supporting the knob of a considerable length, and passed through a glass-tube, a globe of fire was seen to issue out of it. This globe gradually ascended up the glass-tube till it came to the top of the knob, where it settled, turning swiftly on its axis, and appearing like a red-hot iron ball of three quarters of an inch diameter. On continuing to turn the machine, it gradually descended into the jar; which it had no sooner done, than there ensued a most violent explosion and flash, the jar being discharged and broken at the same time. This experiment, however, is singular in its kind; for neither the gentleman who performed it, nor any other, has yet been able to repeat it. Single as it is, however, we may yet gather from it, that a fire-ball will be the consequence of a very violent electrification of any substance, provided at the same time that the air be in a very non-conducting state, so that the electricity may not evaporate into it as fast as it is collected; for this would produce only lucid streams and flashes, as in the common experiments with the Leyden phial: and it is probably an inattention to this circumstance which has hitherto prevented the repetition of the experiment above-men-

tioned. The case is the same in thunder-storms, where an excessive accumulation of electric matter always produces fire-balls, the most mischievous kind of lightning, as is explained under that article.

With regard to the uses which fire-balls serve in the system of nature, it is plain that they are the means of preserving the equilibrium in the electric fluid in the atmosphere, which would otherwise produce the most dreadful tempests. Under the article Aurora Borealis, it is shown why there must be a constant current of electric matter through the bowels of the earth from the equator to the poles, and from the poles to the equator through the atmosphere. The great meteors serve for keeping up the equilibrium in this great atmospheric current, while the smaller ones answer a like purpose in the general mass of electric matter dispersed over the surface of the earth, and therefore are seen to move in all directions, as the equilibrium happens to require them in different parts. With regard to those which are observed in the lower regions of the earth, or rolling on the surface of the ground itself, they undoubtedly answer purposes of a similar kind in these lower regions; for as fire-balls in general are produced by a great excess of electricity in one place, there must of course be an equal deficiency in another; and to restore the equilibrium, or, to speak more properly, to prevent a dangerous commotion from taking place throughout the whole mass of electric fluid, the fire-ball breaks forth, and either puts a stop at once to the disturbance by an explosion, or by a silent and invisible evaporation. From some accounts indeed it would seem that even the large celestial meteors detached part of their substance to accomplish this purpose; though, for the reasons already given, it would seem more probable that they operated by electrifying the atmosphere, or setting the fluid contained in it in motion, so as to produce small fire-balls of itself, rather than by detaching any part of their own bodies to such a distance. Dr. Blagden, in the paper above quoted, gives an account of an appearance of this kind. It was described in a letter to Sir Joseph Banks from the Abbé Mann, director of the academy at Brussels. "It happened (says the Abbé) at Mariékerke, a small village on the coast, about half a mile west of Ollend. The curate of the village was sitting in the dusk of the evening with a friend, when a sudden light surprised them, and, immediately after a small ball of light-coloured flame came through a broken pane of glass, crossed the room where they were sitting, and fixed itself on the chink of a door opposite to the window where it entered, and there died gradually away. It appeared to be a kind of phosphoric light carried along by the current of air. The curate and his friend, greatly surprised at what they saw, apprehended fire in the neighbourhood; but going out, found that the fire which had come in through the window had been detached from a large meteor in its passage."

Fire-Cocks. Churchwardens in London and within the bills of mortality, are to fix fire-cocks at proper distances in streets, and keep a large engine and hand-engine for extinguishing fire, under the penalty of 101. flat. 6 Ann. c. 31.

On the breaking out of any fire in London or Westminster, the constables and beadles of parishes shall repair

pair to the place with their slaves, and assist in extinguishing it, and cause the people to work for that end, &c.