Thra.

Tibet,

laft, because they were defcended from the Perfians. La Tiara tin authors call it indifferently tiara and cidaris. Strabo says, the tiara was in form of a tower; and the fcholiast on Ariftophanes's comedy, Axins, act 1. fcene 2. affirms, that it was adorned with peacock's feathers.

TIARA is alio the name of the pope's triple crown. The tiara and keys are the badges of the papal dignity; the tiara of his civil rank, and the keys of his jurifdiction: for as foon as the pope is dead, his aims are reprefented with the tiara alone, without the keys. The ancient tiara was a round high cap. John XXIII. firft encompaffed it with a crown. Boniface VIII. added a fecond crown; and Benedict XII. a third.

Turday the fudy of the law. In 1648 he was made receiver or clerk of the curfitor fines; and though his attachments were entirely on the fide of the parliament, he declares himself totally unconcerned in all counfels relative to the death of the king: however, on that event, and on the establishment of the commonwealth, he was diverted from profecuting his employments in the law by engaging in public bufinefs. When Cromwell affumed the protectorship, he became fecretary of tate; in 1655, he had the care and charge both of foreign and inland poftage committed to him by the protector; and was afterward fworn one of his privy-council, according to "The humble petition and advice." He was continued in the fame capacities under Richard Cromwell, and until measures were taken for the Restoration; when he made an offer of his services to that end, which, however, were not accepted. May 15th 1660, he was committed to the cuftody of the ferjeant at arms on a charge of high treafon; but being foon released, he retired to Great Milton in Oxfordshire: and though he was afterward often folicited by Charles II. to engage in the adminiftration of public bufinefs, he thought proper to decline the offers. He died in 1668 and was a man of an amiable private character, who in the higheft of his power exercifed all poffible moderation towards perfons of every party. The most authentic teftimony of his abilities is that vaft collection of ftate-papers, feven volumes folio, now in the hands of the public; which place the affairs of Great Britain, and of Europe in general, during that remarkable period in the cleare it light.

THURSDAY, the fifth day of the Chriftian week, but the fixth of that of the Jews.

THUS, FRANKINCENSE, a folid brittle refin, brought to us in little globes or maffes, of a brownish or yellowish colour on the outfide, internally whitish or variegated with whitifh fpecks. It is fuppofed to be the produce of the pine that yields the common turpentine, and to concrete upon the furface of the terebinthinate juice foon after it has iffued from the tree. See INCENSE.

THUYA. See THUJA.

THYMUS, THYME, in botany: A genus of plants belonging to the clafs of didynamia, and order of gymnoff ermia; and in the natural fyftem ranging under the 42d order, Vertillate. The calyx is bilabiate, and its throat clofed with foft hairs. There are 11 fpecies; of which two only are natives of Britain, the ferpyllum and acinas.

1. The ferpyllum, or mother of thyme, has pale red flowers growing on round heads, terminal; the talks are procum. bent, and the leaves plane, obtufe, and ciliated at the bafe. 2. The acinas, or wild bafil, has flowers growing in whirls on fingle footftalks; the talks are ercct and branched; the kaves acute and ferrated. The hymus vulgaris, or garden thyme, is a native of France, Spain, and Italy.-The attachment of bees to this and other aromatic plants is well known. In the experiments male at Upfal, fheep and goats were observed to eat it, and fwine to retufe it.

THYMUS, in anatomy. See ANATOMY, no 114. THYRSUS, in antiquity, the fceptre which the poets put into the hand of Bacchus, and wherewith they furnished the menades in their Bacchanalia. THYRSUS, in botany, a mode of flowering refembling the cone of a pine. It is, fays Linnæus, a panicle contracted into an oval or egg-shaped form. The lower footftalks, which are longer, extend horizontally, whilft the upper ones are fhorter and mount vertically. Lilac and butter-bur furnifh examples.

TIARA, an ornament or habit wherewith the ancient Perfians covered their head; and with which the Armenians and kings of Pontus are reprefented on medals; thele

TIARELLA, in botany: A genus of plants belonging to the class of decandria, and order of digynia; and in the natural fyftem ranging under the 13th order, Succulenta. The calyx is quinquepartite; the corolla pentapetalous, and inferted into the calyx; the petals are entire; the capfule is unilocular and bivalve, the one valve being less than the other. There are two fpecies, the cordifolia and trifoliata.

TIBER, a great river of Italy, which runs through the pope's territories, paffing by Perugia and Orvietto; and having vifited Rome, falls into the Tufcan fea at Oftia, fifteen miles below that city.

TIBET, called by the Tartars Barantola, Bootan, or Tangoot, and by the Chinese Tfang, is fituated between 26° and 39° north latitude; an, according to Abbé Großer, is reckoned to be 640 leagues from caft to welt, and 650 from north to south. It is bounded on the north by the country of the Mongols and the defert of Kobi; on the eaft by China; on the weft by Hindoftan, and on the fouth by the fame country and the kingdom of Ava. In the valleys lying between the lower mountains are many tribes of Indian people; and a dispute happening between the heirs of one of the rajahs or petty princes, one party called. to their affiance the Boutaners, and the other the British. The latter prevailed; and the fame of British valour being carried to the court of Tibet, the 'T'eefhoo Lama, who ruled the itate under the Delai-Lama, at that time in his minority, fent a deputation to Bengal, detiring peace for the prince who had been engaged in war with the British. This was readily granted by the governor; and Mr Bogle was fent ambalador to the court of Tibet, where he reficed feveral months; and after an abfence of a year and a quar ter, returned to Calcutta. The account of this gentleman's expedition hath not been publifhed by himself; but from Mr Stewart's letter to Sir John Pringle, published in the Philofophical Tranfactions, vol. 67. we learn the following · particulars, collected from his papers.

"Mr Bogle divides the territories of the Delai-Lama into two different parts. That which lies immediately contiguous to Bengal, and which is called by the inhabitants Docpo, he diftinguishes by the name of Bootan; and the other, which extends to the northward as far as the frontiers of Tartary, called by the natives Pu, he ftyles Tibet. Bootan is ruled by the Dah Terriah, or Deb Kajah. It is a country of steep and inaccefble mountains, whofe furnmits are crowned with eternal fnow; they are intersected with deep valleys, through which pour numberless torrents that increafe in their courfe, and at laft, gaining t'a plains,· lofe themtelves in the great rivers of Bengal. There mountains are covered down their fides with forefts of stately trees of various forts; fome (fuch as pines, &c.) which are kuown in Europe; others, fuch as are peculiar to the country and climate,

The valleys and fides of the hills which: admit of cultivation are not unfruitful, but produce crops of wheat, barley, and rice. The inhabitants are a flout. and wailike people, of a copper complexion, in fize rather

I.

above:

of the Volgt to Correa on the fea of Japan, the most Tibet extenfive religious dominion, perhaps, on the face of the globe. See LAMA.

above the middle European ftature, hafty and quarrelfome in their temper, and addicted to the ufe of fpirituous liquors; but honeft in their dealings, robbery by violence bein almoft unknown among thein. The chief city is Taffey Seddein fituated on the Patchoo. Tibet begins properly from the top of the great ridge of the Caucafus, and extends from thence in breadth to the confines of Great Tartary, and perhaps to fome of the dominions of the Ruffian empire. The woods, which everywhere cover the mountains in Boutan, are here totally unknown; and, except a few ftraggling trees near the villages, nothing of the fort to be feen. The climate is extremely fevere and rude. At Chamnanning, where he wintered, although it be in latitude 31° 39', only 8° to the northward of Calcutta, he often found the thermometer in his room at 29° by Fahrenheit's fcale; and in the middle of April the ftanding waters were all frozen, and heavy fhowers of fnow perpetually fell. This, no doubt, must be owing to the great elevation of the country, and to the vaft frozen space over which the north wind blows uninterruptedly from the pole, through the vaft deserts of Siberia and Tartary, till it is ftopped by this forinidable wall.

"The Tibetians are of a smaller fize than their fouthern neighbours, and of a lefs robust make. I heir complexions are alio fairer, and many of them have even a ruddiness in their countenances unknown in the other climates of the caft. Those whom Mr Bogle faw at Calcutta appeared to have quite the Tartar face. They are of a mild and cheerful temper; the higher ranks are polite and entertaining in converfation, in which they never mix either ftrained compliments or flattery. The common people, both in Bootan and Tibet, are clothed in coarfe woollen ftuffs of their own manufacture, lined with fuch fkins as they can procure; but the better orders of men are dreffed in European cloth, or China filk, lined with the fineft Siberian furs. The use of linen is totally unknown among them. The chief food of the inhabitants is the milk of their cattle, prepared into cheese, butter, or mixed with the flour of a coarfe barley or of peafe, the only grain which their foil produces; and even thefe articles are in a fcanty proportion: but they are furnithed with rice and wheat from Bengal and other countries in their neighbourhood. They alfo are fupplied with fish from the rivers in their own and the neighbouring provinces, falted and fent into the anterior parts. They have no want of animal food from the cattle, fheep, and hogs, which are raised on their hills; and are not deftitute of game. They have a fingular method of preparing their mutton, by expofing the carcafe entire, after the bowels are taken out, to the fun and bleak northern winds which blow in the months of Auguft and September, without froft, and fo dry up the juices and parch the skin, that the meat will keep uncorrupted for the year round. This they generally eat raw, without any other preparation.

"The religion and political conftitution of this country, which are intimately blended together, would make a confiderable chapter in its hiftory. It fuffices to fay, that at prefent, and ever fince the expulfion of the Eluth Tartars, the kingdom of Tibet is regarded as depending on the empire of China, which they call Cathay; and there actually refide to mandarines, with a garrifon of a thousand Chi. nese, at Lahassa the capital, to fupport the government; but their power does not extend far: and in fact the Lama, whofe empire is founded on the furest grounds, perfon al affection and religious reverence, governs every thing internally with unbounded authority. Every body knows that the Delai Lama is the great object of adoration for the various tribes of heathen Tartars, who roam through the vast tract of continent which ftretches from the banks

"It is an old notion, that the religion of Tibet is a corrupted Chriftianity and even Father Difederii, a Jefuit (but not of the Chinese miffion) who vifted the country about the beginning of this century, thinks he can refolve all their myfteries into ours; and afferts, with a truly myítical penetration, that they have certainly a good rotion of the Trinity, fince in their addrefs to the Deity, they fay as often konciok oik in the plural as konciok in the fingular, and with their rofaries pronounce these words, om, ha, hum. The truth is, that the religion of Tibet, from whatever fource it fprung, is pure and fimple in its fource, conveying very exalted notions of the Deity, with no contemptible fyftem of morality: but in its progrefs it has been greatly altered and corrupted by the inventions of worldly men; a fate we can hardly regret in a system of error, fince we know that that of truth has been subject to the fame. Polygamy, at leaft in the fenfe we commonly receive the word, is not in practice among them; but it exifts in a manner ftill more repugnant to European ideas; for there is a plurality of hulbands, which is firmly established and highly refpected there. In a country where the means of fubfifting a family are not cafily found, it feems not impolitic to al low a fet of brothers to agree in raifing one, which is to be maintained by their joint effts. In fhort, it is ufual in Tibet for the brothers in the family to have a wife in common, and they generally live in great harmony and comfort with her; not but fometimes little diffenfions will arife (as may happen in families conftituted upon different principles), an inflance of which Mr Bogle mentions in the cafe of a modeft and virtuous lady, the wife of half a dozen of the Teefhoo Lama's nephews, who complained to the uncle that the two youngeft of her husbands did not furnish thatfhare of love and benevolence to the common flock which duty and religion required of them. In fhort, however ftrange this cuftom may appear to us, it is an undoubted fact that it prevails in Tibet.

"The manner of beftowing their dead is alfo fingular: they neither put them in the ground like the Europeans, nor burn them like the Hindoos; but expofe them on the bleak pinnacle of fome neighbouring mountain, to be deyoured by wild beafts and birds of prey, or wafted away by time and the viciffitudes of the weather in which they lie. The mangled carcafes and bleached bones lie fcattered about; and amidit this fcene of horror, fome miferable old wretch, man or woman, loft to all feelings but thofe of fuperftition, generally fets up an abode, to perform the difmal office of receiving the bodies, affigning each a place, and gathering up the remains when too widely difperfed."

To the account of Tibet which we have given from the communications of Mr Bogle, we may add the information which we have obtained from a later traveller, Mr Saunders** Paper to furgeon at Boglepoer in Bengal, who made a journey into the Phil Tibet in the year 1783. His obfervations chiefly refpect the natural productions and difeafes of the country.

The plants which Mr Saunders found were almost all European plants, a great number of them being natives of Britain. From the appearance of the hills he concludes that they must contain many ores of metal and pyrites. There are inexhauftible quantities of TINCAL (tee that arti cle), and rock-falt is plentiful; gold-duft is found in great quantities in the beds of rivers, and fometimes in large mafies, lumps, and irregular veins; lead, cinnabar containing a large proportion of quick filver, copper, and iron, he thinks, might easily be procured. But the inhabitants of Tibet have no better fuel than the dung of animals. A coal

Tran. V

LXXIX.

The mine would be a valuable difcovery. We are told, that in Thalus. fome parts of China bordering on Tibet coal is found and ufed as fuel.

It is remarkable that the fame disease prevails at the foot of the mountains of Tibet as in Switzerland at the foot of the Alps, a glandular fwelling in the throat commonly called goitre. This disease has been afcribed to the use of fnowwater, which flows down in ftreams from the mountains in both countries. But in many countries where fnow-water is abundant it does not prevail, and in other places far remote from fnow it is not unfrequent, as in Sumatra. Mr Saunders thinks that it arifes from the air peculiar to the vicinity of certain mountains; and finding the vegetable productions of the mountains of Tibet the fame with thofe of the Alps, that they also may have their influence. An analysis of the water where this disease prevails might throw fome light on the fubject. We have heard it attributed to the impregnation of water with tufa. This very extraordinary difcafe has been little attended to, 'from obvious reasons; it is unaccompanied with pain, feldom fatal, and generally confined to the poorer fort of people. The tumor is unfightly, and grows to a troublesome fize, being often as large as a perfon's head. It is certainly nat exaggerating to fay, that one in fix of the Rung pore diftrict, and country of Bootan, has the disease.

As those who labour most, and are the leaft protected from the changes of weather, are moft fubject to the disease, we univerfally find it in Bootan more common with the women than men. It generally appears in Bpotan at the age of thirteen or fourteen, and in Bengal at the age of eleven or twelve; fo that in both countries the difeafe fhows itself about the age of puberty. I do not believe this disease has ever been removed, though a mercurial course seemed to check its progrefs, but did not prevent ita advance after intermitting the use of mercury. An attention to the primary caufe will firft lead to a proper method of treating the disease; a change of fituation for a fhort while, at that particular period when it appears, might be the means of preventing it.

The venereal disease is not uncommon in Tibet ; and what will perhaps furprize the phyfician, the inhabitants are acquainted with the effects of mercury, and with a method of preparing it fo as to render it a safe and efficacious remedy. They know how to deprive it of its metallic form by mixing it with alum, nitre, and vermilion, and expofing it to a certain degree of heat, which they judge of by weighing the fuel.

The language fpoken in Tibet is different from that of the Tartars. The aftronomers are acquainted with the motion of the heavenly bodies, and able to calculate eclipses: but the lamas are generally ignorant; few of them can read, much lefs understand their ancient books.

TIBULLUS (Aulus Albius), a Roman knight, and a celebrated Latin poet, was born at Rome 43 B. C. He was the friend of Horace, Ovid, Macer, and other great men in the reign of Auguftus. He accompanied Meffala Corvinus in his expedition against the island of Corcyra: `but falling fick, and being unable to support the fatigues of war on account of the weakness of his conftitution, he quitted the profeffion of arms, and returned to Rome, where he died before the year 17; when Ovid fhowed his grief for his death by writing a fine elegy upon him. Tibullus wrote four books of elegies, which are still extant: they are written in a tender and agreeable ftyle, and in very elevant Latin. Muret and Jofeph Scaliger have written earned and curious commentaries on the works of this poet. The best edition of Tibullus is that of Janus Bronckhufius, published at Amfterdam in 1708, in one VOL. XVIII. Part II.

volume quarto. We have an English poetical verfion by Tibur Mr Grainger.

TIBUR, (anc. geog.) a town of Latium, pleasantly fituate on the Anio. Here Horace had his villa and houfe; and here he wished to end his days. Here Adrian built an extraordinary villa called Tiburtina, infcribed with the names of the provinces and of the most confiderable places, (Spartian); near which Zenobia had a house called Zenobia, (Trebellius, Pollio). Hither Auguftus often retreated on account of its falubrity, (Suetonius): for which it is greatly commended, (Martial). Anciently, when the Romans had far extended their territory, it was the utmost place of banishment, (Ovid). It had a temple of Hercules; and therefore called Herculeum. In the temple was a li brary, (A. Gellius). Now Tivoli in the Campagna di Roma on the Teverone.

TICINUS, (anc. geog.) a river in Infubria, rifing in mount Adula, traverfing the Lacus Verbanus fouthwards, and falling into the Po near Ticinum. Between this river and the Po Hannibal gained his first victory over the Romans under P. Scipio. The general himself escaped with the utmoft difficulty, and that by the bravery of his fon the firft Scipio Africanus. Now the Tefino, rifing in mount Godard, running fouth through the Lago Maggiore and Milan, by Pavia, into the Po.

TICK, in zoology. See ACARUS.

TICKELL (Thomas), an excellent English poet, was the fon of the Reverend Richard Tickell, and was born in 1686, at Bridekirk in Cumberland. He was educated at Queen's college, Oxford, of which he was made fellow; and while he continued at that univerfity, he addressed to Mr Addifon a complimentary copy of verses on his Opera of Rofamond, which introduced him to an acquaintance with that gentle man, who difcovering his merit, became his fincere friend. On Mr Addison's being made secretary of state, he appointed Mr Tickell his under-fecretary; and on his being obliged to refign that office on account of his ill health, he recommended him fo effectually to Mr Craggs his fucceffor, that he was continued in his poft till that gentleman's death. In 1724 Mr Tickell was appointed fecretary to the lords juftices in Ireland, and enjoyed that place as long as he lived. He wrote fome poems, which, when feparately published, met with a favourable reception, and paffed through feveral editions: they are now printed in the fecond volume of The Minor Poets. After Mr Addison's death Mr Tickell had the care of the edition of his works printed in 4 vols 4to; to which he prefixed an account of Mr Addifon's life, and a poem on his death. Mr Tickell died in the year 1740.

TICKERA, a confiderable article of merchandise in
Fezzan in Africa; it is valued by travellers as a portable
and highly falubrious food. It is a preparation of pounded
dates, and the meal of Indian corn, formed into a paste, and
highly dried in an oven.
See COREOPSL8.

TICKSEED, SUN-FLOWER.
TICUNAS. See Poison, p. 266.
TIDE, is a word which expreffes that rifing and falling
of the waters which are observed on all maritime coafts.

There is a certain depth of the waters of the ocean which would obtain if all were at reft: but obfervation fhows that they are continually varying from this level, and that fome of these variations are regular and periodical.

ift, It is obferved, that on the shores of the ocean, and in bays, creeks, and harbours, which communicate freely with the ocean, the waters rife up above this mean height twice a day, and as often fink below it, forming what is called a FLOOD and an EBB, a HIGH and a LOW WATER. The whole interval between high and low water is called a TIDE; 3 T

the

Tide.

Tide. the water is faid to FLow and to EB3; and the rifing is called the FLOOD-TIDE, and the falling is called the EBB

TIDE.

2d, It is obferved, that this rife and fall of the waters is variable in quantity. At Plymouth, for inftance, it is fometimes 21 feet between the greatest and leaft depth of the water in one day, and fometimes only 12 feet.

Thefe different heights of tide are obferved to fueceed each other in a regular feries, diminishing from the greateft to the leaft, and then increasing from the leaft to the greateft. The greatest is called a SPRING TIDE, and the leaft is called a NEAP TIDE.

3d, This feries is completed in about 15 days. More careful obfervation fhows that two feriefes are completed in the exact time of a lunation. For the fpring tide in any place is obferved to happen precifely at a certain interval of time (generally between two and three days) after new or full moon, and the neap tide at a certain interval after half moon; or, more accurately speaking, it is observed that the fpring tide always happens when the moon has got a certain number of degrees eastward of the line of conjunction and oppofition, and the neap tide happens when she is a certain number of degrees from her firft or last quadrature. Thus the whole series of tides appears to be regulated by

the moon.

4th, It is obferved that high water happens at new and full moon when the moon has a certain determined pofition with respect to the meridian of the place of obfervation, preceding or following the moon's fouthing a certain interval of time; which is conftant with refpect to that place, but very different in different places.

5th, The time of high water in any place appears to be regulated by the moon; for the interval between the time of high water and the moon's fouthing never changes above three quarters of an hour, whereas the interval between the time of high water and noon changes fix hours in the course of a fortnight.

6th, The interval between two fucceeding high waters is variable. It is leaft of all about new and full moon, and greatest when the moon is in her quadratures. As two high waters happen every day, we may call the double of their interval a TIDE DAY, as we call the diurnal revolution of the moon a lunar day. The tide day is fhorteft about new aud full moon, being then about 24" 37′; about the time of the moon's quadratures it is 25 27. Thefe values are taken from a mean of many obfervations made at Barbadoes by Dr Maikelyne.

7th, The tides in fimilar circumftances are greatest when the moon is at her fmalleft diftance from the earth, or in her perigee, and, gradually diminishing, are smalleft when the is in her apogee.

8th, The fame remark is made with refpect to the fun's distance, and the greatest tides are observed during the winter months of Europe.

9th, The tides in any part of the ocean increase as the moon, by changing her declination, approaches the zehith of that place.

10th, The tides which happen while the moon is above the horizon are greater than the tides of the fame day when

the moon is below the horizon.

Such are the regular phenomena of the tides. They are important to all commercial nations, and have therefore been much attended to. It is of the tides, in all probability, that the Bible speaks, when God is faid to fet bounds to the fea, and to fay" this far fhall it go, and no farther."

Homer is the earlieft profane author who fpeaks of the tides. Indeed it is not very clear that it is of them that he fpeaks (in the XIIth book of the Odyssey) when he speaks of

Charybdis, which rifes and retires thrice in every day. Hero. dotus and Diodorus Siculus foeak more diftinctly of the tides in the Red Sea. Pytheas of Marfeilles is the first who says any thing of their caufe. According to Strabo he had been in Britain, where he must have obferved the tides of the ocean. Plutarch fays exprefsly that Pytheas afcribed them to the moon. It is fomewhat wonderful that Aristotle says fo little about the tides. The army of Alexander, his pu pil, were ftartled at their first appearance to them near the Perfian Gulph; and we should have thought that Aristotle would be well informed of all that had been obferved there. But there are only three paffages concerning them in all Ariftotle's writings, and they are very trivial. In one place he fpeaks of great tides obferved in the north of Europe; in another, he mentions their having been afcribed by fome to the moon; and in a third, he fays, that the tide in a great fea exceeds that in a small one.

The Greeks had little opportunity of obferving the tides. The conquefts and the commerce of the Romans gave them more acquaintance with them. Cæfar fpeaks of them in the 4th book of his Gallic War. Strabo, after Polidonius, claffes the phenomena into daily, monthly, and annual. He obferves, that the fea rifes as the moon gets near the meridian, whether above or below the horizon, and falls again as fhe rifes or falls; also, that the tides increase at the time of new and full moon, and are greatcft at the fummer folftice. Pliny explains the phenomena at fome length; and says, that both the fun and moon are their cause, dragging the wa ters along with them (B. II. c. 97). Seneca (Nat. Quest. III. 28.) fpeaks of the tides with correctness; and Macrobius (Somn. Scip. I. 6.) gives a very accurate defcription of their motions.

It is impoffible that fuch phenomena fhould not exercife human curiofity as to their caufe. Plutarch (Plaut. Phil. III. 17), Galileo (Syft. Mund. Dial. 4.), Riccioli in his Almage, ii. p. 374, and Gaffendi, ii. p. 27. have collected most of the notions of their predeceffors on the fubject; but they are of fo little importance, that they do not deferve our notice. Kepler fpeaks more like a philofopher (De Stella Martis, and Epit. Aftron. p. 555). He fays that all bodies attract each other, and that the waters of the ocean would all go to the moon were they not retained by the attraction of the earth; and then goes on to explain their clevation under the moon and on the oppofite fide, becaule the earth is lefs attracted by the moon than the nearer waters, but more than the waters which are more remote. The honour of a complete explanation of the tides was referved for Sir Ifaac Newton. He laid hold of this clafs of phenomena as the most inconteftable proof of univerfal gravitation, and has given a most beautiful and fynoptical view of the whole fubject; contenting himself, however, with merely exhibiting the chief confequences of the general principle, and applying it to the phenomena with fingu. lar addrefs. But the wide fteps taken by this great philofopher in his inveftigation leave ordinary readers frequently at fault: many of his affumptions require the greatest mathematical knowledge to fatisfy us of their truth. The academy of Paris therefore proposed to illustrate this among other parts of the principles of natural philofophy, and published the theory of the tides as a prize problem. This produced three excellent differtations, by M'Laurin, Dan. Bernoulli, and Euler. Aided by these, and chiefly by the fecond, we fhall here give a phyfical theory, and accommodate it to the purposes of navigation by giving the rules of calculation. We have demonftrated in our differtations on the phyfical principles of the celeftial motions, that it is an unexcepted fact, that every particle of matter in the folar fyftem is actually deflected toward every other particle; and

particle be diminished by a force acting in the direction CF, Tile. and proportional to the distance of the particle from C, and fuch, that when C is equal to o O, the force acting on c is equal to the force acting on o. In order that the former equilibrium may be reftored after this diminution of the gravitation of the column fC, it is plain that more water mult he poured into the oblique tower Ff. All this is evident when we confider the matter hydroftatically. The gravitation of the particle e may be reprefented by oO; but the diminution of the preffure occasioned by this at O is reprefented by Cc.

that the deflection of a particle of matter toward any diftant fphere is proportional to the quantity of matter in that fphere directly, and to the fquare of the diftance of the particle from the centre of that sphere inversely: and having found that the heavinefs of a piece of terreftrial matter is nothing but the fuppofed opponent to the force which we exert in carrying this piece of matter, we conceive it as poffeffing a property, that is, diftinguishing quality, manifelted by its being gravis or heavy. This is heavinels, gravitas, gravity; and the manifeftation of this quality, or the event in which it is feen, whether it be directly falling, or deflecting in a parabolic curve, or ftretching a coiled spring, or breaking a rope, or fimply preffing on its fupport, is gravitatio, gravitation; and the body is faid to gravitate. When all obftacles are removed from the body, as when we cut the ftring by which a ftone is hung, it moves directly downwards, tendit ad terram. Si difcindatur funis, tenderet lapis ad terram. Dum vero funis integer perflet, lapis terram verfus niti cenfetur. By fome metaphyfical procefs, which it is needlefs at prefent to trace, this nifus ad motum has been called a tendency in our language. Indeed the word has now come to fignify the energy of any active quality in thofe cafes where its fimpleft and moft immediate manifeftation is prevented by fome obftacle. The ftone is now faid to tend toward the earth, though it does not actually approach it, being withheld by the ftring. The ftre ching the ftring in a direction perpendicular to the horizon is conceived as a full manifeftation of this tendency. This tendency, this inergy of its heavinefs, is therefore named by the word which diftinguishes the quality; and it is called gravitation, and it is faid to gravitate.

But Sir Ifaac Newton difcovered that this deflection of a heavy body differs in no respect from that general deflection obferved in all the bodies of the folar fyftem. For 16 feet, which is the deflection of a ftone in one fecond, has the very fame proportion to 5th of an inch, which is the fimultaneous deflection of the moon, that the square of the moon's diftance from the centre of the earth has to the fquare of the ftone's diftance from it, namely, that of 3600

to 1.

Thus we are enabled to compare all the effects of the mutual tendencies of the heavenly bodies with the tendency of gravity, whofe effects and measures are familiar to us.

If the earth were a sphere covered to a great depth with water, the water. would form a concentric fpherical thell; for the gravitation of every particle of its furface would then be directed to the centre, and would be equal. The curvature of its furface therefore would be every where the fame, that is, it would be the uniform curvature of a sphere. It has been demonftrated in former articles, after Sir Ifaac Newton, that the gravitation of a particle C (fig. 1.) to the centre O, is to that of a particle E at the furface as as CO to EO. In like manner the gravitation of o is to that of p as o O to pO. If therefore EO and Op are two communicating canals, of equal lengths, the water in both would be in equilibrio, because each column would exert the fame total preffure at O. But if the gravitation of each particle in pO be diminished by a certain proportion, fuch asyth of its whole weight, it is plain that the total pref fure of the column pO will be th part lefs than that of the column EO. Therefore they will no longer be in equilibrio. The weight of the column EO will prevail; and if a hollow tower Pp be built at the mouth of the pit po, the water will fink in EO and rife in Op, till both are again in equilibrio, exerting equal total preffures at O. Or we may prevent the finking at E by pouring in more water into the tower Pp. The fame thing muft happen in the canal fe perpendicular to EO, if the gravitation of every

Hence we can collect this much, that the whole diminution of preffure at C is to the whole diminution of preffure at O as the fum of all the lines c C to the fum of all the lines o O, that is, as ƒC2 to p0. But the weight of the fmall quantity of water added in each tower is diminished in the fame proportion; therefore the quantity added at Ff. must be to the quantity added at Pp as fC to pO. Therefore we muft have Ff: Pp=1C:p O, and the points E, F, P, must be in the circumference of an ellipfe, of which PO and EO are the tranfverfe and conjugate femiaxes,

What we have here fuppofed concerning the diminution of gravity in these canals is a thing which really obtains in nature. It was demonftrated, when treating of the PRECES, SION of the Equinoxes, that if the fun or moon lie in the di rection OP, at a very great distance, there refults from the unequal gravitation of the different particles of the earth a diminution of the gravity of each particle; which diminution, is in a direction parallel to OP, and proportional to the diftance of the particle from a plane paffing through the centre of the earth at right angles to the line OP.

Thus it happens that the waters of the ocean have their equilibrium disturbed by the unequal gravitation of their different particles to the fun or to the moon; and this equilibrium cannot be reftored till the waters come in from all hands, and rife up around the line joining the centres of the earth and of the luminary. The spherical ocean must acquire the form of a prolate fpheroid generated by the revolution of an ellipse round its tranfverfe axis. The waters will be highest in that place which has the luminary in its zenith, and in the antipodes to that place; and they will be moft depreffed in all thofe places which have the luminary in their horizon. P and P will be the poles, and EOQ will be the equator of this prolate spheroid.

Mr Fergufon, in his Aftronomy, affigns another cause of this arrangement, viz. the difference of the centrifugal forces of the different particles of water, while the earth is turning round the common centre of gravity of the earth and moon. This, however, is a mistake. It would be juft if the earth and moon were attached to the ends of a rod, and the earth kept always the fame face toward the moon.

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canals