John Platts

CURIOSITIES RESPECTING VARIOUS PHENOMENA, OR APPEARANCES IN NATURE.—(Continued.)

Spots in the Sun—Diminution of the Sun—Parhelia, or Mock Suns—Eclipses—Halo, or Corona; and similar Appearances—Falling or Shooting Star—Volcanoes in the Moon.

Spots in the Sun.—The following account of the spots in the sun is taken from a French paper.

“The spots were seen for the first time in 1611; and nearly about the same time by J. Fabricius, at Wittenberg, by the Jesuit Scheiner, and by Galileo. This great man watched their course with so much attention, and so well developed their phenomena, that very little has been since added to the descriptions which he gave, except more precise measures. The spots of the sun are at present viewed with astronomical telescopes, in which the great brilliancy of that luminary is mitigated, and not effaced, by the coloured glass placed between the telescope and the eye. There are in the interior of the telescope, at the focus of the object, some very fine threads stretched crosswise, and moveable parallel to each other, by means of which the distance of the spot from the nearest border of the sun’s disk may be ascertained, which determines its position on the disk at the moment of observation. By following in this manner the same spot for several days, it is perceived to change its place. Its size also varies much. The spots sometimes grow thinner, and disperse from one day to another: and hence it is, that, though in one month rather a large number was visible, in the following only two are to be seen. But during the whole time of their presence they pursue a regular course, of which the aspects are common to all.

“When they first come in sight, they appear on the sun’s border, like a slender thread. In proportion as they advance towards the middle of the disk, they appear, from day to day, to enlarge in the direction of their movement. They then decrease periodically; and if they last long enough to traverse the whole disk, they go off by the opposite side, narrowing to a single thread. These appearances are evidently such as a small body, adhering to a spherical surface, and revolving with or upon that surface, must present. The diminution of the spots, in proportion as they approximate the borders of the disk, results from this—that they then project more obliquely, and are only seen sidewise; but when in the middle of the disk, they are seen in their full extent. In fine, upon comparing the direction and rapidity of their course, it soon becomes evident, that the supposition of their adhering to the body of the sun is the only admissible one. On thus tracing the route of all those which appear, it is ascertained that they move in courses exactly parallel, describing circles which all have their centre on a common axis, passing through the centre of the sun. The size of these circles varies on different points of the disk, according to the same laws as on a sphere; and the rate of movement is modified in such a way, that all the circles are run through in equal times. This perfect concordance of revolution in spots so changeable in other respects, evidently shews that they must be attached to one and the same round body, which makes them revolve altogether with a common motion. Hence it has been concluded, that the sun revolves upon itself with the general motion of these spots, that is, in twenty-five days and a half, in like manner as our earth revolves in twenty-four hours. The same calculation, applied to the spots which have been discovered on the other planets, has in like manner made us acquainted with their rotation.

PARHELIA, OR MOCK SUN.—Page 673.

THE IGNIS FATUUS, Will-with-a-Wisp, or Jack-with-a-Lantern.—Page 644.

“As to the nature of these solar spots, it is absolutely unknown. Herschel is of opinion, that luminous clouds float in the inflamed atmosphere of this luminary, as clouds of vapour float in ours. He supposes that the body of the sun is opaque and dark; and that the black spots observed there at intervals, are merely the summits of very elevated mountains, which the solar clouds permit us to see between their openings. Other astronomers think that the globe of the sun is on fire, and that the spots are merely immense scoria, launched on the surface of that mass by some terrible explosions, of which our terrestrial volcanoes afford but a feeble picture. But whatever may be thought of these conjectures, it seems sufficient for us to know, that the solar spots are trifling compared with the immense mass of that body; and that the eruptions, of which they are perhaps the effect, take place at too great a distance from our earth to produce the least effect upon it. Generally speaking, the physical state of our little world is incomparably more stable and steady than its moral state.”

Diminution of the Sun.—Baron Lindeneau, who recently published a work on the diminution of the solar mass, says, that the sun may have been imperceptibly subject to successive diminution since the science of astronomy has been cultivated. Baron Lindeneau supposes the sun’s diameter to be 800,000 miles, 4,204,000,000 feet, or nearly 2000 seconds. We have not, he observes, hitherto possessed any instrument for measuring the diameter of the heavenly bodies to a second. The sun may therefore diminish 12,000 of its diameter, or 2,102,000 feet, without the possibility of being perceived. Supposing the sun to diminish daily two feet, it would require three thousand years to render the diminution of a second of its diameter visible.

Account of those singular Appearances, called, Parhelia, or Mock Suns.—

As when two suns appear in th’ azure sky,
Mounted in Phoebus’ chariot fierie bright:
Both darting forth fair beams to each man’s eye;
And both adorn’d with lamps of flaming light,
All that behold such strange prodigious sight,
Not knowing nature’s work, nor what to weene,
Are wrapt with wonder, and with rare affrighte.
Spenser.

A Parhelion is a meteor in form of a bright light, appearing on one side of the sun. Phenomena of this kind have been mentioned both by the ancients and moderns. Aristotle observes, that in general they are seen only when the sun is near the horizon, though he takes notice of two that were seen in Bosphorus from morning till evening; and Pliny has related the times when such phenomena were observed at Rome. Gassendi says, that in 1635-1636 he often saw one mock sun. Two were observed by M. de la Hire in 1689; and the same number by Cassini in 1693; by Mr. Grey in 1700, and by Dr. Halley in 1702; but the most celebrated phenomena of this kind were seen at Rome by Scheiner; by Muschenbroek at Utrecht; and by Hevelius at Ledan. By the two former, four mock suns were observed; and by the latter, seven. Parhelia are apparently of the same size with the sun, though not always of the same brightness, nor even of the same shape; and when a number appear at once, there is some difference in both respects among them. Externally they are tinged with colours like the rainbow; and many have a long fiery tail opposite the sun, but paler towards the extremity. Parhelia are generally accompanied with coronas, some of which are tinged with rainbow colours, but others are white. (See Halo.) They differ in number and size; but all agree in breadth, which is that of the apparent diameter of the sun. A very large white circle, parallel to the horizon, generally passes through all the parhelia; and, if it were entire, it would go through the centre of the sun. Sometimes there are arcs of lesser circles concentric to this, touching those coloured circles which surround the sun. They are also tinged with colours, and contain other parhelia. Other circles are said to have been obliquely situated with respect to all these. The order of the colours in these circles is the same as in the rainbow; but on the inside, with respect to the sun, they are red, as is also observed in many haloes. Parhelia have been visible for one, two, three, and four hours together; and in North America, they are said to continue some days, and to be visible from sunrise to sunset. When the parhelia disappear, it sometimes rains, or snow falls in the form of oblong spiculÆ, as Maraldi, Weidler, Krafft, and others, have observed; and because the air in North America abounds with such frozen spiculÆ, which are even visible to the eye, according to Ellis and Middleton, such particles have been thought to be the cause of all coronas and parhelia.

Mr. Wales says, that at Churchill, in Hudson’s Bay, the rising of the sun is always preceded by two long streams of red light, one on each side, and about twenty degrees distant from him. These rise as the sun rises; and as they grow longer, they begin to bend towards each other, till they meet directly over the sun, just as he rises, forming there a parhelion, or mock sun. These two streams of light, he says, seem to have their source in two other parhelia, which rise with the true sun; and in winter, when the sun never rises above the haze or fog, which he says is constantly seen near the horizon, all these accompany him the whole day, and set with him. Once or twice he saw a fourth parhelion, directly under the sun; but this is not common. These facts being constant, are very valuable, and may throw great light on the theory of these remarkable phenomena. Sometimes parhelia appear in a different manner; as when three suns have been seen in the same vertical circle, well defined, and touching one another. The true sun was in the middle, and the lowest touched the horizon, and they set one after the other. This appearance was seen by Maleziew, in 1722. Other appearances similar to this are recited by Mr. Muschenbroek. Sometimes the sun has risen or set with a luminous tail projecting from him, of the same breadth with his diameter, and perpendicular to the horizon. Such an appearance was seen by Cassini in 1672 and 1692; by De la Hire in 1702; and by Mr. Ellis in Hudson’s Bay. As M. FeuilÉe was walking on the banks of the river La Plata, he saw the sun rising over the river, with a luminous tail projecting downwards, which continued till he was six degrees high. ParaselÆ, or mock moons, have also been seen, accompanied with tails and coloured circles, like those which accompany the parhelia. An account of several, and a particular description of a fine appearance of this kind, may be seen in Muschenbroek.

The following account of this phenomenon is extracted from a pamphlet, entitled, ‘Somewhat written by occasion of Three Sunnes’ seene, at Tregorie, in Cornwall, the 22nd of December last; with other memorable occurrents in other places. Imprinted 1622: 20 pages small 4to.’

“Since this strange apparition, namely, upon the 10th of January last, there happened in Devonshire, yet not farre from the other place, being on the edge of Cornwalle, another wonder, which, did as much affrighte the eares of men, as this did their eyes: for in the afternoone of that day, being the Thursday after Twelfth-day, there were heard in the aire unusuall cracks or claps of thunder, resembling in all points the sound of many drums together, sometimes beating charges, sometimes retreats, sometimes marches, and all other points of warre: which, after it had continued a good time, it seemed that the same thunder did most lively expresse many volleyes of small-shot, and afterwards the like volleyes of ordnance, with so great and yet so distinct noyse, that many of them who dwelt neare the sea, went toward the shore to see what it might meane, as verily supposing there had beene some sea fight neere upon that coast. These severall fearfull noyses were againe and againe renewed in the same order, till at length with an horrible and extraordinary cracke of thunder, there fell in a ground of one Robert Pierce, where there were divers workemen planting apple-trees, (which ground lay neere the house of one Master George Chidley,) a thunder-bolt, if I may so call it, being a stone of three foot and an halfe in length, of two foot and an halfe in breadth, and one foot and an halfe in thicknesse, the substance whereof was in hardnesse and colour not much unlike a flint, as appeares by many pieces thereof, which are shewed up and downe by many credible and honest gentlemen, who, with their own hands, brake them off from the maine stone. After the fall of this stone, which with the weight thereof was cleane buried in the ground above a yard deepe, the thunder ceased, and people began as much to won—at that which they now saw, as they had lately done at that, which with so much feare and amazement they had heard.”

Observations on Eclipses of the Sun and Moon.—

Give me the ways of wand’ring stars to know,
The depths of heav’n above and earth below;
Teach me the various labours of the Moon,
And whence proceed th’ Eclipses of the Sun.
Virg. Georg. ii

The deprivation of the light of the sun, or some heavenly body, by the interposition of another heavenly body between our sight and it is, called an Eclipse. Thus, eclipses of the sun happen by the moon’s intervening between it and the earth; by which means the shadow of the moon falls upon the earth, when the latitude of the moon does not prevent it, by elevating her orb above, or depressing it below the earth. On the other hand, an eclipse of the moon can only happen when the earth is interposed between the sun and it; for then, if the latitude of the moon does not prevent it, the shadow of the earth may fall on the moon, and thereby cause either a partial, or total eclipse. A total eclipse of the sun or moon, is when their whole bodies are obscured; and a partial one, is when part only of their bodies is darkened: again, a central eclipse is when it is not only total, but the eclipsed body passes through the centre of the shadow.

As total solar eclipses are by no means common, we shall give an interesting description of one, by Dr. Stukeley, sent to his friend, the celebrated Dr. Edmund Halley.

“According to my promise, I send you what I observed of the solar eclipse, though I fear it will not be of any great use to you. I was not prepared with any instruments for measuring time or the like, and proposed to myself only to watch all the appearances that nature would present to the naked eye upon so remarkable an occasion, and which generally are overlooked, or but grossly regarded. I chose for my station a place called Haradon Hill, two miles eastward from Amsbury, and full east from the opening of Stonehenge avenue, to which it is as the point of view. Before me lay the vast plain where that celebrated work stands, and I knew that the eclipse would appear directly over it; besides, I had the advantage of a very extensive prospect every way, this being the highest hill hereabouts, and nearest the middle of the shadow. Full west of me, and beyond Stonehenge, is a pretty copped hill, like the top of a cone, lifting itself above the horizon; this is Clay-hill, near Warminster, twenty miles distant, and near the central line of darkness, which must come from thence, so that I could have notice enough beforehand of its approach. Abraham Sturgis and Stephen Ewens, both of this place, and sensible men, were with me. Though it was very cloudy, yet now and then we had gleams of sunshine, rather more than I could perceive at any other place around us. These two persons, looking through smoked glasses, while I was taking some bearings of the country with a circumferentor, both confidently affirmed the eclipse was begun, when, by my watch, I found it just half an hour after five; and accordingly from thence the progress of it was visible, and very often to the naked eye; the thin clouds doing the office of glasses. From the time of the sun’s body being half covered, there was a very conspicuous circular iris round the sun, with perfect colours. On all sides we beheld the shepherds hurrying their flocks into fold, the darkness coming on; for they expected nothing less than a total eclipse for an hour and a quarter.

“When the sun looked very sharp like a new moon, the sky was pretty clear in that spot; but soon after a thicker cloud covered it, at which time the iris vanished; the copped hill before-mentioned grew very dark, together with the horizon on both sides, that is, to the north and south, and looked blue, just as it appears at the declension of day. We had scarcely time to tell them, when Salisbury steeple, six miles off southward, became very black; the copped hill was quite lost, and a most gloomy night with full career came upon us: at this instant we lost sight of the sun, whose place among the clouds was hitherto sufficiently distinguishable, but now not the least trace of it was to be found, any more than if really absent: then I saw by my watch, though with difficulty, and only by help of some light from the northern quarter, that it was six hours thirty-five minutes: just before this, the whole compass of the heavens and earth looked of a lurid complexion, properly speaking, for it was black and blue, only on the earth upon the horizon the blue prevailed; there was likewise in the heavens, among the clouds, much green interspersed, so that the whole appearance was really very dreadful, and as symptoms of sickening nature.“Now I perceived we were involved in total and palpable darkness, as I may aptly call it; for though it came quickly, yet I was so intent, that I could perceive its steps, and feel it as it were drop upon us, and fall on the right shoulder (we looking westward) like a great dark mantle, or coverlet of a bed, thrown over us, or like the drawing of a curtain on that side. The horses we held in our hands were very sensible of it, and crowded close to us, startling with great surprise; and as much as I could see of the men’s faces that stood by me, they had a horrible aspect. At this instant I looked around me, not without exclamations of admiration, and could discern colours in the heavens, but the earth had lost its blue, and was wholly black. For some time, among the clouds, there were visible streaks of rays, tending to the place of the sun as their centre; but immediately after, the whole appearance of earth and sky was entirely black: of all things I ever saw in my life, or can by imagination fancy, it was a sight the most tremendous.

“Towards the north-west, whence the eclipse came, I could not in the least find any distinction in the horizon between heaven and earth, for a good breadth of about sixty degrees, or more; nor the town of Amsbury underneath us, nor scarcely the ground we trod on. I turned myself round several times during this total darkness, and remarked at a good distance from the west on both sides, that is, to the north and south, the horizon very perfectly; the earth being black, the lower parts of the heavens light; for the darkness above hung over us like a canopy, almost reaching the horizon in those parts, or as if made with skirts of a lighter colour; so that the upper edges of all the hills were as a black line, and I knew them very distinctly by their shape or profile; and northward, I saw perfectly, that the interval of light and darkness in the horizon was between Martinsal-hill and St. Ann’s-hill; but southward it was more indefinite. I do not mean that the verge of the shadow passed between those hills, which were but twelve miles distant from us; but, so far I could distinguish the horizon; beyond it not at all. The reason of it was this; the elevation of ground I was upon gave me an opportunity of seeing the light of the heavens beyond the shadow; nevertheless, this verge of light looked of a dead yellowish, and greenish colour; it was broader to the north than south; but the southern was of a tawny colour: at this time behind us, or eastward toward London, it was dark too, where otherwise I could see the hills beyond Andover; for the foremost end of the shadow was past thither; so that the whole horizon was now divided into four parts of unequal bulk, and degrees of light and dark; the part to the north-west broadest and blackest, to the south-west lightest and longest. All the change I could perceive during the totality, was, that the horizon by degrees drew into two parts, light and dark: the northern hemisphere growing still longer, lighter, and broader; and the two opposite dark parts uniting into one, and swallowing up the southern enlightened part.

“As at the beginning the shade came feelingly upon our right shoulders, so now the light from the north, where it opened as it were; though I could discern no defined light or shade upon the earth that way, which I earnestly watched for, yet it was manifestly by degrees, and with oscillation, going back a little, and quickly advancing further, till at length, upon the first lucid point appearing in the heavens, where the sun was, I could distinguish pretty plainly a rim of light running alongside of us a good while together, or sweeping by at our elbows from west to east. Just then, having reason to suppose the totality ended with us, I looked on my watch, and found it to be full three minutes and a half more. Now the hill-tops changed their black into blue again, and I could distinguish an horizon where the centre of darkness was before: the men cried out, they saw the copped-hill again, which they had eagerly looked for; but still it continued dark to the south-east, yet I cannot say that ever the horizon that way was undistinguishable. Immediately we heard the larks chirping, and singing very briskly, for joy of the restored luminary, after all things had been hushed into a most profound and universal silence. The heavens and earth now appeared exactly like morning before sunrise, of a greyish cast, but rather more blue interspersed; and the earth, so far as the verge of the hill reached, was of a dark green, or russet colour.

“As soon as the sun emerged, the clouds grew thicker, and the light was very little amended for a minute or more, like a cloudy morning slowly advancing. After about the middle of the totality, and so after the emersion of the sun, we saw Venus very plainly, but no other star. Salisbury steeple now appeared; but the clouds never removing, we could take no account of it afterwards; but in the evening it lightened very much. I hastened home to write this letter, and the impression was so vivid upon my mind, that I am sure, I could for some days after have written the same account of it, and very precisely. After supper I made a drawing of it from my imagination, upon the same paper on which I had taken a prospect of the country before.

“I must confess to you, that I was (I believe) the only person in England, that regretted not the cloudiness of the day, which added so much to the solemnity of the sight, and which incomparably exceeded, in my apprehension, that of 1715, which I saw very perfectly from the top of Boston steeple, in Lincolnshire, where the air was very clear; but the night of this was more complete and dreadful: there, indeed, I saw both sides of the shadow come from a great distance, and pass beyond us to a considerable extent; but this eclipse had much more of variety and majestic terror; so that I cannot but felicitate myself upon the opportunity of seeing these two rare accidents of nature, in so different a manner. Yet I should willingly have lost this pleasure, for your more valuable advantage of perfecting the noble theory of the celestial bodies, which, last time, you gave the world so nice a calculation of; and I wish the sky had now as much favoured us for an addition to your honour and great skill, which I doubt not to be as exact in this as before.”

We now proceed to describe The Halo, or Corona; and similar Appearances.—An Halo is a luminous circle surrounding the sun, moon, planets, or fixed stars. Occasionally these circles are white, and sometimes they are coloured like the rainbow. Sometimes one only is visible, and at others several concentric halos appear at the same time. Mr. Huygens observed red next the sun, and a pale blue outwards. Sometimes they are red on the inside, and white on the outside. In France, one was observed in 1683, the middle of which was white; after which followed a border of red, next to it was blue, then green, and the outermost circle was a bright red. In 1728, one was seen of a pale red outwardly, then followed yellow, and then green, terminated by a white. In Holland, M. Muschenbroek says, fifty may be seen in the day-time, almost every year; but they are difficult to be observed, except the eye be so situated, that not the body of the sun, but only the neighbouring parts of the heavens, can be seen. Mr. Middleton says, that this phenomenon is very frequent in North America; for that there is generally one or two about the sun every week, and as many about the moon every month. Halos round the sun are very frequent in Russia. M. Æpinus says, that from the 23d of April, 1758, to the 20th of September, he himself had observed no less than twenty-six, and that he has sometimes seen twice as many in the same space of time.

Similar, in some respects, to the halo, was the remarkable appearance which M. Bouguer describes, as observed on the top of Mount Pichinca, in the Cordilleras. When the sun was just rising behind them, so as to appear white, each of them saw his own shadow projected upon it, and no other. The distance was such, that all the parts of the shadow were easily distinguishable, as the arms, the legs, and the head; but what surprised them most was, that the head was adorned with a kind of glory, consisting of three or four small concentric crowns, of a very lively colour, each exhibiting all the varieties of the primary rainbow, and having the circle of red on the outside. The intervals between these circles continued equal, though the diameters of them all were constantly changing. The last of them was very faint; and at a considerable distance was another great white circle, which surrounded the whole. This phenomenon never appeared but in a cloud consisting of frozen particles, and never in drops of rain like the rainbow. When the sun was not in the horizon, only part of the white circle was visible, as M. Bouquer frequently observed afterwards. Similar to this curious appearance, was one seen by Dr. M’Fait in Scotland; who observed a rainbow round his shadow in the mist, when he was upon an eminence above it. In this situation the whole country round seemed buried under a vast deluge, and nothing but the tops of distant hills appeared here and there above the flood. In those upper regions, the air, he says, is at that time very pure and agreeable. At another time he observed a double range of colours round his shadow. The colours of the outermost range were broad and very distinct, and every where about two feet distant from the shadow. Then there was a darkish interval, and after that another narrower range of colours, closely surrounding the shadow, which was very much contracted. He thinks that these ranges of colours are caused by the inflection of the rays of light, the same that occasions the ring of light which surrounds the shadow of all bodies, observed by M. Maraldi, and others.

We next proceed to the phenomenon generally called Falling or Shooting Star.—This is a luminous meteor, darting rapidly through the air, and resembling a star falling from the heavens. The explication of this phenomenon had puzzled all philosophers, till the modern discoveries in electricity led to the most probable account of it. Signior Beccari makes it pretty evident, that it is an electrical appearance, and recites the following fact in proof of his opinion. About an hour after sunset, he, and some friends that were with him, observed a falling star directing its course towards them, and apparently growing larger and larger, but it disappeared not far from them. When it vanished, it left their faces, hands, and clothes, with the earth, and all the neighbouring objects, suddenly illuminated with a diffused and lambent light, but not attended with any noise. During their surprise at this appearance, a servant informed them, that he had seen a light shine suddenly in the garden, and especially upon the streams which he was throwing to water it. All these appearances were evidently electrical; and Beccari was confirmed in his conjecture, that electricity was the cause of them, by the quantity of electric matter which he had seen gradually advancing towards a kite he had elevated, which had very much the appearance of a falling star. Sometimes, also, he saw a kind of glory round the kite, which followed it when it changed its place, but left some light, for a small space of time, in the place it had quitted.

Captain Bagnold says, whilst passing through the straits of Bahama, in the autumn of 1799, he witnessed the following singular atmospheric phenomenon.

“It was a fine star-light morning, about two o’clock, the atmosphere remarkably clear, with a light air from the north-east; the sky to windward, from north-north-east to south-south-east, was illuminated by a profusion of those meteors, vulgarly denominated falling stars, but of a description far more vivid than those usually seen in the higher latitudes; the head of each was an oblong ignited mass, followed by a long luminous tail, which, after three or four seconds, gradually vanished. They were formed, to all appearance, in the air, at an elevation of from thirty-five to sixty-four degrees, none being observed in the zenith, and few to commence nearer the horizon than the first-mentioned angles. At the mean of these elevations, the greatest numbers were seen darting in different directions, forming portions of a large curve, all slightly inclined to the horizon. Multitudes were constantly visible at the same moment, and they succeeded each other so rapidly, that the eye of the spectator was kept in motion between the above points of the compass. In about ten minutes they became less frequent, and at length ceased altogether.

“The apparent distance of this phenomenon would, by a seaman, be estimated at fifteen or twenty miles; and if it really was what I have always considered it, namely, a nocturnal shower of meteoric stones, it was perhaps fortunate for all on board, that we were not within the sphere of its action: whatever it was, never shall I forget the splendour of the spectacle.”—See Humboldt’s Personal Narrative, volume III. page 331, 335.

We close this chapter with An Account of Three Volcanoes in the Moon; by Dr. Herschel.

“It will be necessary to say a few words by way of introduction to the account I have to give of some appearances upon the moon. The phenomena of nature, especially those that fall under the inspection of the astronomer, are to be viewed, not only with the usual attention to facts as they occur, but with the eye of reason and experience. In this we are, however, not allowed to depart from plain appearances, though their origin and signification should be indicated by the most characterizing features. Thus, when we see on the surface of the moon a great number of elevations, from half a mile to a mile and a half in height, we are strictly entitled to call them mountains; but when we attend to their particular shape, in which many of them resemble the craters of our volcanoes, and thence argue that they owe their origin to the same cause which has modelled many of these, we may be said to see by analogy, or with the eye of reason. Now, in this latter case, though it may be convenient, in speaking of phenomena, to use expressions that can only be justified by reasoning upon the facts themselves, it will certainly be the safest way not to neglect a full description of them, that it may appear to others how far we have been authorized to use the mental eye. This being premised, I may safely proceed to give my observations.

“April 19th, 1787, 10h. 36', sidereal time: I perceive three volcanoes in different places of the dark part of the new moon. Two of them are either already nearly extinct, or otherwise in a state of going to break out; which, perhaps, may be decided next lunation. The third shews an actual eruption of fire, or luminous matter. I measured the distance of the crater from the northern limb of the moon, and found it 3' 57.3. Its light is much brighter than the nucleus of the comet which M. Mechain discovered at Paris the 10th of this month.—April 20th, 1787, 10h. 2', sidereal time: The volcano burns with greater violence than last night. I believe its diameter cannot be less than 3, by comparing it with that of the Georgian planet: as Jupiter was near at hand, I turned the telescope to his third satellite, and estimated the diameter of the burning part of the volcano to be equal to at least twice that of the satellite. Hence we may compute that the shining or burning matter must be above three miles in diameter. It is of an irregular round figure, and very sharply defined on the edges. The other two volcanoes are much farther towards the centre of the moon, and resemble large pretty faint nebulÆ, that are gradually much brighter in the middle; but no well-defined luminous spot can be discerned in them. These three spots are plainly to be distinguished from the rest of the marks upon the moon; for the reflection of the sun’s rays from the earth is, in its present situation, sufficiently bright, with a ten-feet reflector, to shew the moon’s spots, even the darkest of them; nor did I perceive any similar phenomena last lunation, though I then viewed the same places with the same instrument.

“The appearance of what I have called the actual fire, or eruption of a volcano, exactly resembled a small piece of burning charcoal, when it is covered by a very thin coat of white ashes, which frequently adhere to it after it has been some time ignited; and it had a degree of brightness about as strong as that with which such a coal would be seen to glow in faint daylight. All the adjacent parts of the volcanic mountain seemed to be faintly illuminated by the eruption, and were gradually more obscure as they lay at a greater distance from the crater.

“This eruption resembled much that which I saw on the fourth of May, in the year 1783; an account of which, with many remarkable particulars relating to volcanic mountains in the moon, I shall take an early opportunity of communicating to the Royal Society. It differed, however, considerably in magnitude and brightness; for the volcano of the year 1783, though much brighter than that which is now burning, was not near so large in the dimensions of its eruption; the former seen in the telescope resembled a star of the fourth magnitude, as it appears to the natural eye: this, on the contrary, shews a visible disk of luminous matter, very different from the sparkling brightness of star-light.”