veries have been made of late years, particularly in the South Seas, of iflands which owe their birth to volcanic explofions; and fome, indeed, where the volcanic fire ftill operates. I am led to believe, that upon further examination, moft of the elevated iflands at a confiderable diftance from continents would be found to have a volcanic origin; as the low and flat islands appear in general to have been formed of the Ipoils of fea productions, fuch as corals, madrepores, &c. But I will stop here, and not deviate from the plan which I have hitherto ftrictly followed, of reporting faithfully to my learned brethren of the Royal Society fuch facts only as come immediately under my own obfervation, and as I think may be worthy of their notice, and leave them at full liberty to reafon upon them. "We may flatter ourfelves, as a very great progrefs has been made of late years in the knowledge of volcanoes, that by combining fuch obfervations as we are already in poffeffion of, with thofe which may be made hereafter, in the four quarters of the world (in all of which 'nature feems to have operated in a like manner), a much better theory of the earth may be cftablished than the miferable ones that have hitherto appeared. "Those who have not had an opportunity of examining a volcanic country, as I have for more than twenty years, would little fufpect, that many curious productions and combinations of lava's and tuffa's were of a volcanic origin; efpecially when they have undergone various chemical operations of nature, fome of which, as I have mentioned in a former communication as well as in this, have been capa ble of converting tuffa's, lava's, and pumice stone, into the pureft clay. "I have remarked, that young obfervers in this branch of natural history are but too apt to fall into the dangerous error of limiting the order of nature to their confined ideas: for example, fhould they fufpect a mountain to have been a volcano, they immediately climb to its fummit to feek for the crater, and if they neither find one, or any figns of lava or pumice stone, directly conclude fuch a mountain not to be volcanic: whereas, only fuppofe Mount Etna to have ceafed erupting for many ages, and that half of its conical part fhould have mouldered away by time (which would naturally be the confequence) and the harder parts remain in points, forming an immenfe circuit of mountains (Etna extending at its bafis more than one hundred and fifty miles); fuch an obferver as I have just mentioned would certainly not find a crater on the top of any of these mountains, and his ideas would be too limited to conceive, that this whole range of mountains were only part of what once conftituted a complete cone and crater of a volcano. cannot be too ftrongly recommended to obfervers in this, as well as in every other branch of natural hiftory, not to be over hafty in their decifions, nor to attribute every production they meet with to a fingle operation of nature, when perhaps it has undergone various, of which I have given examples in the ifland which has been the principal fubject of this letter. That which was one day in a calcareous state and formed by an infect in the fea, becomes vitrified in another, by the action of the volcanic fire, and the addition of fome natural ingredi It ents, ents, fuch as fea falts and weeds, and is again transformed to a pure clay by another curious procefs of nature. The naturalist may indeed decide as to the prefent quality of any natural production; but it would be prefumption in him to decide as to its former ftates. As far as I can judge in this curious country, active nature feems to be conftantly employed in compofing, decompofing, and recompofing; but furely for all-wife and benevolent purposes, though on a fcale perhaps, much too great and extenfive for our weak and limited comprehenfion. "Poftfcript. "The earth is not yet fo perfectly quiet in Calabria and at Meffina, as to encourage the inhabitants to begin to rebuild their houfes, and they continue to live in wooden barracks. There has, however, been no earthquake of confequence during thefe laft three months. My conjecture, that the volcanic matter (which was fuppofed to have occafioned the late earthquakes) had vented itself at the bottom of the fea between Calabria and Sicily, feems to have been verified; for the pilot of one of his Sicilian Majefty's fciabecques, having fome time after the earthquakes caft anchor off the point of Palizzi, where he had often anchored in twenty-five fathom water, found no bottom till he came to fixty-five fathom, and hav ing founded for two miles out at fea towards the point of Spartivento, in Calabria, he ftill found the fame confiderable alteration in the depth of the fea. The inhabitants of Palizzi likewife declare, that during the great earthquake of the th of February, 1783, the fea had frothed and boiled up tremendoufly off their point.' ACCOUNT of a New ELECTRICAL FISH, in a Letter from Lieutenant WILLIAM PATERSON, to Sir JOSEPH BANKS, Bart. P. R. S. [From the fame Publication.] 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 fill, which has hitherto escaped the obfervation of naturalifts, and feems in many respects to differ from the electrical fiflies 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 deferves attention, you will do me the honour of prefenting it to the Royal Society. The fituation of a fubaltern officer, in an army upon foreign service, will, I hope, fufficiently apologize for my fending you so very imperfect a fketch of the fifh, which was made in the field, in a hot climate, under every difadvantage. "The fifh 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 fifh 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 particularly bright; the eyes large, the iris red, its outer edge tinged with yellow. "The island of Johanna is fitu. ated in latitude 12° 13' fouth. The coaft is wholly compofed of coral rock, which are in many places hollowed by the fea. In thefe cavities I found several 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, closed 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 defired the furgeon of the regiment to lay hold of it between his hands; upon doing which he received an evident electrical stroke. Afterwards the adjutant touched it with his finger upon the back, and felt a very flight fhock, but fufficiently strong to afcertain the fact. After fo very imperfect an account, I will not trouble you with any obfervations of my own upon this fingular fish; but beg you will confider this only as a direction to others, who may hereafter visit that ifland, and from their fituation, and knowledge in natural history, may be better able to defcribe the fish, and give an account of its electrical organs." ADVERTISEMENT of the expected RETURN of the COMET of 1532 and 1661, in the Year 1788. By the Rev. NEVIL MASKELYNE, D. D. F. R. S. and Aftronomer Royal. [From the fame Publication. ] HE comet of 1531, 1607, in the year 1759, according to Dr. Halley's prediction in his Synopfis Aftronomia Cometicæ, firft publifhed in the Philofophical Tranfactions in 1705, and re-published with his Afronomical 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 fecond edition he has feemed to leffen the weight of his first conjecture by not repeating it. Pro bably 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 Appian in 1532, might rather de tract from, than add to, the evidence arifing from more certain data. 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 paffages 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 ftyle, which we now ufe, brings out the expected time of the next perihelium to be April 27th, 1 h. 10 in the year 1789. "The periodic times of the comet, which appeared in 1531, 1657, and 1682, having been of 76 and 75 years alternately, Dr. Halley fuppofed that the fubfe. quent 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 feveral months together, equal to one-fiftieth part of the fun upon it, tending to increafe the inclination of the orbit to the plane of the ecliptic, and lengthen the periodic time. Accordingly, 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's action to the latter end of the year 175, or the beginning M. Clairaut, previous to its return, took the pains to calculate the actions both of Jupiter of 159. and Saturn on it during the whole periods from 1607 to 16 2, and from 1682 to 1759, and thence predicted its return to its pesihelium 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 mathemati cian, and his laborious calcula. tions. "The comet in question 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 fhould 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 orbit of Jupiter in the beginning of February 1682, O. S. it was 50° in confequentia of that planet; and when it paffed the or bit 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 fubjected to the effect of retardation through a greater part of its orbit than to that of acceleration, the former would exceed 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 fill 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 fhall be better informed after C after the end of this year, from the anfwers to the prize queftion propofed by the Royal Academy of Sciences at Paris, to compute the disturbances of the comet of 1532 and 1661, and thence to predict its return. "If it fhould come to its perihelium on the 1ft of January 1789, it might probably be vifible, with a good acromatic telescope, in its defcent to the fun, the middle of September 1788, and fooner or later according as its perihelium should 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 south declination; fo that perfons refiding nearer the equator than we do, or in fouth latitude, will have an opportunity of difcovering it before us. to be wished that it may be first feen by fome aftronomer in fuch a fituation, and furnished with proper inftruments for fettling its place in the heavens, the earliest good obfervations being most valuable for determining its elliptic orbit, and proving its identity with the comets of 1532 and 1651. The Cape of Good Hope would be an excellent fituation for this purpose. It is "In order to affift aftronomers in looking out for this comet, I have here given its heliocentric and geocentric longitudes and latitudes and correfpondent distances from the fun and earth, on fuppofition that it fhall come to its perihelium on January 1ft, 1783. 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 longitudes and latitudes and diftances from the earth must be recomputed accordingly. The calculations are made for a parabolic orbit from the elements determined by Dr. Halley from Hevelius's obfervations in 1651, only allowing for the preceffion of the equinoxes. The elements made ufe of were as follows: Time of perihelium January 1, 1789, at noon. Perihelium diftance, 0,44851. 18'. Inclination of orbit to the ecliptic 32° 36'. Perihelium forwarder in orbit than the afcending node 33° 28'. Its motion is direct. In the following table are fet down the computed places of the comet, on fuppofition that it fhall return to its perihelium January 1, 1789, at noon. |