TEOROLOGICAL; and he makes a number of judicious and learned obfervations on each head. The effay is written in a declamatory but vivid ftyle, and contains a variety of curious information, peculiarly interefting to an inhabitant of the Ame rican States.

The Tranfactions commence with four fhort papers by the late Dr. FRANKLIN, which, probably, were never defigned for publication. Of thefe the firft and fourth may be claffed together as containing the fame ideas; the former entitled "Conjectures concerning the Formation of the Earth, &c. in a letter to the Abbe Soulavie, and the latter Queries and Conjectures relating to Magnetifm, and the Theory of the Earth, in a letter to Mr. Bodoin.' The Doctor fuppofes the central mafs of the earth to be a fluid, probably air, in a ftate fo extremely condensed as to float the heaviest fubftances; and that the waves raised and propagated on this internal ocean, by fubterraneous fires or the fudden converfion of water into steam, shake the incumbent fhell, produce earthquakes, and occafion those diftant rumbling founds which announce their approach. He thinks that the remains of animals and plants now peculiar to the torrid zone, found in the most northern climates, afford a proof that the earth has changed its poles; which hypothefis, in his opinion, accounts the most readily for the deluge, and for the various changes which have happened on the face of our globe. The Doctor feems to confound the poles of the earth's axis with thofe of the terreftrial magnet; for he conjectures that the approximation of fome large comet might, by its fuperior magnetic power, have deranged the poles of our globe, and thereby have produced thofe ftriking revolutions on the furface. We need fcarcely obferve that a change of the magnetic poles does by no means imply an alteration in the plane of the earth's rotatory motion. Dr. FRANKLIN farther fuppofes that the iron ore in our globe is the gradual production of time, that it derived its magnetiím from fome external caufe, and that the magnetic power is perhaps diffufed through the univerfal system.

It is enough to mention thefe conjectures, which may amuse a philofopher in a vacant hour. That the matter of the earth is not homogeneous, but increases in denfity towards the centre, is inferred by M. de la Place from a comparison of the obfervations made in different places to determine a degree of the meridian. Whether this nucleus be fluid, it is more difficult to decide. It cannot be air in its elastic form; fince, under the enormous compreflion, the particles would be fo approximated as moft probably to affume a new conftitution. With regard to the origin of earthquakes, they have long been afcribed to the fudden formation of vapour by the bursting of the waters of the

ocean

ocean into the fiery chambers of volcanos, and Mr. Mitchel has written an ingenious effay on this fubject. Earthquakes are generally accompanied with volcanic eruptions; and, from a variety of facts, it appears that the globe is cavernous at leaft beneath the furface, and that fubterraneous communications exift between the moft diftant craters.

Art. 2. A new and curious Theory of Light and Heat; in & Letter from Dr. B. FRANKLIN to D. Rittenhouse, Esq.

The Doctor prefumes that univerfal space is filled by a fubtil fluid, whofe motion or vibration forms light; that the union of this fluid with bodies conftitutes heat, maintains fluidity, and fupplies the materials for growth; that it communicates to the particles of air the repulfion eflential to the elastic fate; that it has aftrong attraction to water, with which it rifes by its bouyancy in the form of vapour, but feparates in the higher regions of the atmosphere, and forms a ftratum that furrounds and accompanies our globe; that the fluid ftratum, extending in fome meaLure through the air to the furface of the earth, caufes the fenfa tion of light by communicating the vibrations which it receives. from the fun; that, by thefe vibrations during the day, heat is amaffed in bodies, but which partly efcapes during the night; and, finally, that fire makes the greateft part of the substance of combustible bodies, and, being feparated by the digeftion of food, produces the natural warmth of animals.-Thele conjectures, which have fcarcely the merit of novelty, are in general fo unfubftantially founded, that it would be fuperfluous to attempt a ferious refutation of them.

Art. 3. Defcription of the Procefs to be obferved in making large Sheets of Paper in the Chinese Manner, with one fmao.b Surface.

Dr. FRANKLIN firft defcribes the tedious operations employed in Europe for this purpose, with which, from his early habits of life, he was well acquainted. The Chinese procets is thus explained:

In China, if they would have sheets, fuppofe of four and an half ells long and one and an half ell wide, they have two large vats, each five ells long and two ells wide, made of brick, lined with a plafter that holds water. In these the stuff is mixed ready to work.

Between thefe vats is built a kiln or ftove, with two inclining fides; each fide fomething larger than the fheet of paper; they are covered with a fine ftucco that takes a polith, and are fo contrived as to be well heated by a small fire circulating in the walls.

The mould is made with thin but deep fides, that it may be both light and fiff. It is fufpended at each end with cords that pass over pallies fattened to the ceiling, their ends connected with a counterpoise nearly equal to the weight of the mould.

• Two

Two men, one at each end of the mould, lifting it out of the water by help of the counterpoife, turn it, and apply it with the fluff for the theet, to the fmooth furface of the ftove, against which they prefs it, to force out great part of the water through the wires. The heat of the wall foon evaporates the reft, and a boy takes off the dried fheet by rolling it up. The fide next the flove receives the even polish of the ftucco, and is thereby fitted to receive the impreffion of five prints. If a degree of fizing is required, a decoction of rice is mixed with the ftuff in the vat.'

Art. 5. Explanation of a fingular Phenomenon, first observed by Dr. Franklin, and not hitherto fatisfactorily accounted for; à Letter from Mr. R. PATTERSON to Dr. B. Rush.

The phænomenon is this:-If a tumbler, filled about twothirds with equal parts of water and oil, be gently moved backwards and forwards, or made to ofcillate like a pendulum, the furface of the water in contact with the oil will be thrown into violent undulations, while the upper furface of the oil remains comparatively placid. Mr. PATTERSON justly rejects the explications given of this curious fact by Dr. Percival and Dr. Wall in the Manchester Tranfactions, as inadequate or unintelligible. The explication which he offers is entirely fatisfactory, and is fo fimple as to excite furprize that it had not occurred to former inquirers. He attributes the phænomenon to the fmall difference between the fpecific gravity of oil and that of water. If a fubftance, whether fluid or folid, have exactly the fame denfity with a fluid, it will continue fufpended, indifferent to its pofition, and liable to be difplaced by the fmalleft disturbance. Every approach to this equality is attended with a fimilar property, only in a lefs degree. In the present inftance, if a portion of water rife above the furface, an equal bulk of oil must defcend; and the force adequate to produce this exchange is merely the difference between the weights of these two portions. It is otherwife with the surface of the oil contiguous to the air; not to mention that the tenacity of the oil checks the formation of waves, and that the difturbing forces are principally expended on the internal undulations.On these principles, Mr. PATTERSON accounts for the common practice, in winter, of fwinging in the hand a mug of beer that has ftood before the fire, to mix intimately the cold and warm portions of the liquor.

Art. 6. Account of an Earthy Subftance found near the Falls of Niagara, and vulgarly called the Spray of the Falls; with fome Remarks on the Falls. By ROBERT MCAUSLAND, M. D.

The fubftance here denoted is found plentifully about the bottom of the falls, in maflès either loofe or adhering to the rocks, of a friable or folid confiftence, and of various fizes and fhapes.

fhapes. It is fometimes of a foliated texture, and conftantly hardens by expofure to the air. From a comparison of the facts and experiments related in this paper, it appears to be compofed of the minute particles of a felenitous earth abraded from the rocks immediately above the falls, borne along by the impetuofity of the torrent, and afterward depofited in the eddies or ftil! water. The vulgar notion, that the river is purified by the tremendous concuffion which it fuffers at that celebrated cataract, is indeed totally inadmiffible. If the extraneous matter floated in the water, agitation would help to keep it fufpended and if it were chemically combined, no impulfe could ever detach it. It is a fact that at Niagara, thirteen or fourteen miles below the falls, the waters of the St. Laurence are of a better quality than at Fort Schloffer, a mile and a half above them: but this may be attributed to the influx of many falubrious ftreams from the marfhy grounds. Befides, at Fort Erie, twenty miles above the falls, the water is reckoned not inferior to that at Niagara. The hard quality is probably owing to the folution of faline fubftances contained in the rocks a little above the falls.-Dr. M'CAUSLAND obferves that the bed of the rock from which the river precipitates itself is not horizontal, but inclined from the north-eaft to the fouth-weft; infomuch that, on the one fide, he found the height of the fall to be 163 feet, and on the other, only 143; which accounts for the diverfity in the measurements hitherto given. It is univerfally believed, in the neighbourhood, that the cataract has gradually changed its place, and broken down the rock for a space of fix or feven miles. Suppofing this retroceffion to be pretty regular, the fmall quantity obferved in nine years by Dr. M'CAUSLAND would give an immenfe antiquity to the American continent.— Several affertions occur in this paper, which appear to us unphilofophical, but we cannot afford the time neceffary for controverting them.

Art. 7. Obfervations on the Probabilities of the Duration of Human Life, and the Progrefs of Population in the United States of America, in a Letter from WILLIAM BARTON, Efq. to David Rittenboufe, LL. D. Prefident, A. P. S.

Art. 16. Poftfcript to the above.

The industrious author of this paper difcovers an intimate acquaintance with the works of all the able authors who, in Europe, have employed their talents on the curious and interefting fubject of the probabilities of human life. He endeavours to thew, from the few facts which he could collect, that the climate of America is more congenial to man than that of Europe; that marriages are more fruitful in the new world;

and

and that, in every period of life, a fmaller proportion is there cut off by disease. The data from which he draws thefe conclufions, fo flattering to an American, are, it must be confeffed, very flender; and great allowance is to be made for that warm partiality which is fo. natural in the citizens of a rising state. We would alfo obferve that Mr. BARTON's computations are chiefly founded on registers made at Salem in Maflachufets, and in two parishes at Philadelphia, the healthieft parts of America, and inhabited by the fobereft people. Nor is there any fair comparison hetween the open towns of America and the large compact cities of Europe, which have generally ferved for the bafis of calculations. Nay, admitting the facts alledged in this paper, we might draw an oppofite conclufion. Of a thoufand perfons born, 218 die between the age of twenty and forty at Salem, and only 127 in Europe. This proves the extreme prevalence in America of acute difeafes, which commit their ravages in the prime of years; and never, furely, is death attended with images fo deeply afflicting as when it strikes in the active season of life. In vain would Mr. BARTON fupport his affertions by recounting inftances of extreme longevity in Ame rica; these occur in every country, though rarely. They are to be deemed fports of nature, which neither prove the falubrity of the climate nor the robuftness of the individual. Ex amples might be given of perfons, with a fickly conftitution, who have extended the term of their lives beyond a century.

Art. 8. Extract of a Letter from ANDREW ELLICOTT L David Rittenhoufe, Efq. dated at Pittsburg, November 5, 1787, containing Obfervatious at Lake Erie.

On the evening of Sept. 12, there was a fine aurora boreaus. The next day was cloudy, but without rain. About noon, the low peninfula, called Prefque-ifle, which, at its then distance of twenty-five miles, is commonly invifible, was defcried from the border of the lake, confiderably elevated above the horizon; and, viewed through an achromatic telescope, the branches of the trees could be plainly discovered. It is very fingular that the peninfula was frequently feen double; the images, one above the other, feparating and coinciding repeatedly, like those obferved in shifting the index of a Hadley's quadrant. In the evening, it began to blow a fresh breeze; which, in the following days, increafed into a moft violent hurricane.

Thefe diftinct facts afford fome data for the investigation of the curious phænomenon which failors term looming. We will offer the following attempt at an explication:-It is easy to perceive that, owing to the fucceffive increafe of rarity at different heights in the atmofphere, the rays of light tranfmitted

from