cinders, I have conftantly observed that the lava has foon after made its appearance, either by boiling over the crater, or forcing its paffage through crevices in the conical part of the volcano. As long as I remain in this country, and have the neceffary affiftance of the abovementioned ingenious Monk (who is as excellent a draughtsman as he is an accurate and diligent obferver) the Vefuvian diary fhall be continued; and I hope one day to have the honour of prefenting these curious manufcripts (which begin now to be voluminous) to the Royal Society, if it fhould think them worthy of a place in the Library of the Society."

Sir,

W

HILE at the island of Johanna, one of the Comora iflands, in my way to the Eaft-Indies, with the 98th regiment, I met with an electrical fish, which has hitherto escaped the observation of naturalifts, and feems in many refpects to differ from the electrical fishes already defcribed; which induces me to fend you the following account of it, with a very imperfect drawing, and to beg that, if you think it deserves attention, you will do me the honour of presenting it to the Royal Society. The fituation of a fubaltern officer, in an army upon foreign fervice, will, I hope, fufficiently apologize for my fending you fo very imperfect a sketch of the fish, which was made in the field, in a hot climate, under every difadvantage.

The fish is feven inches long, two inches and a half broad, has a long projecting mouth, and feems to be of the genus Tetrodon. The back of the fish is a dark brown colour, the belly part of fea-green, the fides yellow, and the fins and tail of a fandy green. The body is interfperfed with red, green, and white fpots, the white ones particularly bright; the eyes large, the iris red, its outer edge tinged with yellow.

The island of Johanna is fituated in latitude 12° 13′ fouth. The coaft is wholly compofed of coral rocks, which are in many places hollowed by the fea. In these cavities I found feveral of the electrical fishes. The water is about 56° or 60° of heat of Fahrenheit's thermometer. I caught two of them in a linen bag, clofed up at one end, and open at the other. In attempting to take one of them in my hand, it gave me fo fevere an electrical fhock, that I was obliged to quit my hold. I however fecured them both in the linen bag, and carried them to the camp, which was about two miles diftant. Upon my arrival there, one of them was found to be dead, and the other in a very weak state, which made me anxious to prove, by the evidence of others, that it poffeffed the powers of electricity, while it was yet alive. I had it put into a tub of water, and desired the furgeon of the regiment to lay hold of it between his hands; upon doing which he received an evident electrical ftroke. Afterwards the adjutant touched it with his finger upon the back, and felt a very flight fhock, but fufficiently ftrong to afcertain the fact.

After fo very imperfect an account, I will not trouble you with

any

any obfervations of my own upon this fingular fish; but beg you will confider this only as a direction to others who may hereafter vifit that ifland, and from their fituation, and knowledge in natural hiftory, may be better able to defcribe the fish, and give an account of its electrical organs.

I have the honour to be, with great esteem, &c.

W. PATERSON, Lieutenant 98th regiment.

Advertisement of the expected return of the Comet of 1532 and 1661 in the year 1788. By the Rev. Nevil Mafkelyne, D. D. F. R. S. and Aftronomer Royal. From the fame.

T

HE comet of 1531, 1607, and 1682, having returned in the year 1759, according to Dr. Halley's prediction in his Synopfis Aftromomie Cometica, first published in the Philofophical Tranfactions in 1705, and re-published with his Aftronomical Tables in 1749, there is no reason to doubt that all the other comets will return after their proper periods, according to the remark of the fame author.

In the first edition of the Synopfis he fuppofed the comets of 1532 and 1661, from the fimilarity of the elements of their orbits, to be one and the fame; but in the fecond edition he has feemed to leffen the weight of his firft conjecture by not repeating it. Probably he thought it beft to establish this new point in aftronomy, the doctrine of the revolution of comets in elliptic orbits, as all philofophical matters in the beginning fhould be, on the most certain grounds; and feared

that the, vague obfervations of the comet, made by Apian in 1532, might rather detract from, than add to, the evidence arifing from more certain data. Aftronomers, however, have generally acquiefced in his first conjecture of the comets of 1532 and 1661 being one and the fame, and to expect its return to its perihelium accordingly in 1789.

The interval between the paffa

ges of the comet by the perihelium in 1532 and 1661 is 128 years, 89 days, 1 hour, 29 minutes, (32 of the years being biffextile) which, added to the time of the perihelium in 1661, together with 11 days to reduce it from the Julian to the Gregorian ftile, which we now use, brings out the expected time of the next perihelium to be April 27th, h. 1o in the year 1789.

The periodic times of the comet, which appeared in 1531, 1607, and 1682, having been of 76 and 75 years alternately, Dr. Halley fuppofed, that the fubfequent period would be of 76 years, and that it would return in the year 1758; but, upon confidering its near approach to Jupiter, in its defcent towards the fun in the fummer of 1681, he found, that the action of Jupiter upon the comet was, for several months together, equal to one-fiftieth part of the fun upon it, tending to increase the inclination of the orbit to the plane of the ecliptic, and lengthen the periodic time. Aceordingly, the inclination of the orbit was found by the obfervations made in the following year 1682 to be 22' greater than in the year 1607. The effect of the augmentation of the periodic time could not be feen till the next return, which he fuppofed would be protracted by Ju

piter'a

piter's action to the latter end of the year 1758, or the beginning of 1759. M. Clairaut, previous to its return, took the pains to calculate the actions both of Jupiter and Saturn on it during the whole periods from 1607 to 1682, and from 1682 to 1759, and thence predicted its return to its perihelium by the middle of April; it came about the middle of March, only a month fooner, which was a fufficient approximation to the truth in fo delicate a matter, and did honour to this great mathematician, and his laborious calculations.

The comet in queftion is alfo, from the pofition of its orbit, liable to be much disturbed both by Jupiter and Saturn, particularly in its afcent from the fun after paffing its perihelium, if they should happen to be near it, when it approaches to or croffes their orbits; because it is very near the plane of them at that time. When it paffed the or-bit of Jupiter in the beginning of February 1682, O. S. it was 50° in confequentia of that planet; and when it paffed the orbit of Saturn in the beginning of October 1663, it was 17° in confequentia of it. Hence its motion would be accelerated while it was approaching towards the orbit of either planet by its feparate action, and retarded when it had paffed its orbit; but, as it would be subjected to the effect of retardation through a greater part of its orbit than to that of acceleration, the former would ex

ceed the latter, and confequently the periodic time would be fhortened; but probably not much, on account of the confiderable distance of the comet from the planets when it paffed by them; and therefore we may ftill expect it to return to its perihelium in the beginning of the year 1789, or the latter end of the year 1788, and certainly fome time before the 27th of April 1789. But of this we shall be better informed after the end of this year, from the answers to the prize queftion proposed by the Royal Academy of Sciences at Paris, to compute the difturbances of the comet of 1532 and 1661, and thence to predict its return *.

If it should come to its perihelium on the 1ft of January 1789, it might probably be vifible, with a good achromatic telescope, in its defcent to the fun, the middle of September 1788, and fooner or la ter, according as its perihelium thould 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; so 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 firft seen by fome aftronomer in such a fituation, and furnished with proper inftruments for fettling its place in the heavens, the earliest good observations being most valuable for de

termining

terming its elliptic orbit, and proving its identity with the comets of 1532 and 1661. The Cape of Good Hope would be an excellent fituation for this purpose.

In order to affift aftronomers in looking out for this comet, I have here given its heliocentric and geocentric longitudes and latitudes, and correfpondent diftances from the fun and earth, on fuppofition that it fhall come to its perihelium on January 1, 1789. But if that fhould 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 longi

The laft obfervation 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 telescope of 9-feet focal length, with an aperture of 1,65 inch; then, because the diameter of the aperture of a telescope fufficient to render the comet equally visible fhould be as the product of its diftances from the fun and earth, and the product of the numbers abovementioned 0,986 and 1,37 is 1,35, we fhall have the following analogy to find the aperture of a refracting telescope fufficient to fhew 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.

left into one point of view the memorable inftances of long-lived perfons, whofe ages are recorded by monumental infcriptions, biographical writings, or even by the public prints. The only judicious attempt I have yet feen of this kind, was by the ingenious Mr. Whitehurt, a few years ago, in his Inquiry into the Origin and Formation of the Earth. To the examples of longevity mentioned by him, as collected by a perfon of veracity from the above fources, I have now added fundry remarkable instances of a fimilar kind, as they have occurred to me in the course of reading; and have annexed the authorities, (fo far as was practicable) that you may be enabled to judge of the degree of credibility, that may feem due to the refpective facts, and of the allowance which it may appear neceffary to make, for that natural propenfity, which mankind have ever betrayed for the marvellous. Now, admitting that many of the ages may have been fomewhat exaggerated, yet ftill there can be no poflible doubt, that even thefe have extended far beyond the ordinary period of life, and' may therefore be entitled to a place in the following tables, which I fubmit to your confideration, as a fmall fpecimen of what might be more worthy your attention, if conducted hereafter on a larger fcale, and purfued with chronological accuracy.