them one to another, and by adjusting the Whole to fome Standard Period, regulate the entire Succeffion of paft Tranfactions.

P. I fee it evidently; and as the Measures and Periods of Time seem naturally to come in firft, being those by which we compute from the others, I fhould be glad that you begin with them.

G. I defign fo. And firft, as the Idea of Time in general is acquired, by confidering the Parts of Duration as existing in Succeffion, and diftant from one another by several Intervals; fo the Idea of any particular Time or Length of Duration, as a Day, a Month, a Year, &c. is obtained, by obferving certain Appearances uniformly returning at regular and feemingly equi-diftant Periods. For thus we get the Notion of equal Spaces, and by variously multiplying and combining thefe, can form to ourselves different Measures of Time, of different Lengths, according to the Exigency of Things. Now the Motions of the Sun and other Heavenly Bodies, by reafon of their Conftancy and Equability, eafily invited Men to make them the Standard by which to regulate these several Dimenfions, And because the apparent diurnal Revolution of the Sun, was not only conftant and equable, but frequent and of a fhorter Circuit; hence it naturally became the firft Measure of Time, under the Denomination of a Day.

A Day therefore may be defined to be a Divifion of Time, drawn from the Appearance and Difappearance of the Sun; and is of two Kinds, Artificial, and Natural.

The Artificial Day, which seems to be that primarily meant by the Word Day, is the Time of Light, or of the Sun's Stay above the Horizon, determined by his Rifing and Setting: In Oppofition to which, the Time of Darkness, or of the Sun's Continuance below the Horizon, from Setting to Rifing again, is called Night.

The Natural, or as it is alfo called the Civil Day, is that Space of Time, wherein the Sun compleats his Circuit round the Earth; or to speak properly and aftronomically, the Time of an entire Revolution of the Equator. Different Nations have acted with great Diversity of Choice, in fixing the Beginning of their Days; fome computing from the Rifing, others from the Setting of the Sun, and others again from his paffing the upper or lower Meridian. Hence the ancient Babylonians, Perfians, Syrians, and moft other Eaftern Nations, with the prefent Inhabitants of the Balearick Iflands, the Greeks, &c. begin their Day with the Sun's Rifing. The

ancient

ancient Athenians and Jews, with the Auftrians, Bohemians, Marcomanni, Silefians, modern Italians, and Chinese, reckon from the Sun's Setting. The ancient Umbri and Arabians, with the modern Aftronomers, from Noon. And the Egyp tians and Romans, with the modern English, French, Dutch, Germans, Spaniards, and Portuguefe, from Midnight. And as different People thus varied as to the Time of beginning the Day, fo were there different Diftributions and Divifions of it into Parts; fome diftinguishing the Time of the Artificial Day into twelve equal Portions, which therefore in different Seafons of the Years must be of different Lengths. But the Dif tinction that now moft generally prevails, is that of the whole Space of Day and Night into twenty-four Hours, which being fo well known to you already, will need no farther Illuf tration.

P. We have now, I fee, got one Divifion of Time, and I am much mistaken as to your Manner of Proceeding hitherto, or from this fmall Beginning, you will deduce the whole Syftem of Chronology.

G. That indeed is my Defign, and will I hope in the End, turn confiderably to your Advantage. The more fimple and fewer the Principles are with which we fet out, the easier it will be to comprehend the Science built upon them. In fact, all the Periods and Distinctions of Time we meet with in Chronology, are no other than various Combinations of this firft Measure, accommodated to the particular Wants of Mankind, the different Appearances of the Heavens, and the feveral Intervals of past Transactions. Men were no doubt in the Beginning, contented with the fimple Revolution of a Day, and for fome little Time it would well enough serve all the Purposes expected from it. But as the World advanced in Age, and the Intervals between different Tranfactions became large and extended, the Number of Days would multiply fo faft, as foon to difcover the Neceffity of inftituting more comprehenfive Meafures of Time, for the eafy and convenient Computation of thefe longer Spaces. This was done by combining Days into various Systems and Claffes of different Lengths, according to the Exigency of Things, which gave rife to the Inftitution of Months, Years, Olympiads, Luftra, &c. And here again the Motions of the heavenly Bodies were found to be of fingular Ufe. For as before, the Sun, by his appearent Revolution round the Earth, had marked out the Space of a Day; fo the other heavenly Bodies, by their feveral Motions, and a regular Succeffion of varipus Phafes and Appearances, directed Mankind to fuch Combi

nations

nations of their Days, as correfponded with the aforefaid Changes. Thus many of the Diftributions of Time, became not only useful in Computation, but ferved alfo as Measures of the Phenomena and Revolutions of the Heavens. Hence the ftrict Connection between Aftronomy and Chronology, this latter being in a manner wholly founded on the other, and pre-fuppofing fome general Knowledge of it. But altho' in the more early Ages of the World, the Divifions of Time were made to correfpond exactly with the heavenly. Motions, and Rules of Intercalation provided, to bring the Revolutions of different Luminaries to an Agreement; yet it is now found more convenient, to regulate Time by the annual Motion of the Sun only, neglecting, at leaft in Civil Computation, the Lunar Revolutions. But as ancient Chronology cannnot well be understood, without fome Knowledge of thefe alfo, I fhall contrive my following Explications fo as to answer all the Ends of this Science, and give you fome general Idea of it, both in its ancient and modern State.

I have already obferved, that all the Meafures of Time made ufe of in Chronology, are no other than various Combinations. of Days, accommodated to the Exigencies of Things. It therefore now remains, that I take account of the feveral Divifions and Claffes, fhew how they are formed, and in what Manner applied to the regulating of paft Tranfactions, and connecting the Series of Hiftory. The firft and most fimple Combination of this Kind now in ufe, is what we call a Week; and is a Syftem of feven Days continually recurring, inftituted to perpetuate the Memory of the Creation, which being finished in fix Days, the feventh was appointed a Day of Reft, and thenceforward every feventh Day, in Commemoration of this great Event. It is obfervable that not only the Jews, to whom this Inftitution was immediately revealed by God himfelf, but the Syrians alfo, the Egyptians, and most of the oriental Nations, made ufe of this Divifion of Time into Weeks. And this was probably owing to fome Remains of the Tradition of the Creation, which they had ftill retained with divers others. The Names given to the Days of the Week at prefent, are those which were in use among the ancient Heathen Nations, who denominated them from the feven Planets. Thus the first Day was called Sunday, Dies Solis; the fecond Monday, Dies Lunæ, &c. and fo for the reft. The Reafon of thefe Denominations is best derived from the ancient Aftrology. For the Profeffors of that Science, diftributing the Government and Direction of all the Hours of the Week among the feven Planets, fo as

that

that the Government of the firft Hour of the firft Day fell to Saturn, that of the first Hour of the fecond Day to fupiter, &c. they gave each Day the Name of the Planet which prefided over the firft Hour thereof. And thefe Names, with fome little Variation of their Order, are, as I obferved before, ftill retained among the Chriftians of the Weft.

The next confiderable Divifion of Time is into Months. These at their firft Inftitution regarded chiefly the Lunar Motions, and were accordingly regulated by them. But as the Phafes and Appearances of the Moon, are now of little or no Confideration in Civil Computations, a great Alteration has hereby happened in Chronology; and a Month moft commonly means no more, than that Space of Time by which we divide the Year into twelve Parts. Now for the farther Illuftration of this Matter, we are to obferve, that Months may be fitly divided into Aftronomical and Civil. Aftronomical Months, (fo far as it is useful to confider them here,) are those measured by the Revolution and Phases of the Moon. They are again fubdivided into Periodical and Synodical. The Periodical Month is that Space of Time, in which the Moon by her Motion, returneth to the fame Place of her Orb from whence fhe fet out; and confifts of twentyfeven Days, seven Hours, and forty-three Minutes nearly. The Synodical Month is computed from one Conjunction of the Sun and Moon, to the next Conjunction following, and differs from the former in this; that whereas the Periodical Month refpects only the Moon's Orbit, and her entire Revolution in the Zodiac, the Synodical is fo called in refpect of her Conjunction with the Sun. Now after the Time of this Conjunction, the Sun does not continue in the fame Place of the Zodiac, but moves forwards towards the Eaft: upon which it falls out, that the Moon finishing her Course, does not find the Sun again in the fame Point where the left him, he being removed almoft a whole Sign from his former Place. So that to overtake the Sun again, it plainly appears, that a certain Space of Time is requifite befides the Periodical, which makes up the Synodical Month. The Quantity of a Synodical Month is not at all times the fame; because the Sun's apparent Motion being different in different Parts of his Orbit, muft occafion fome Variety in this Respect. The mean Motion however, as Aftronomers call it, is computed at twenty-nine Days and a half. This Synodical Revolution of the Moon, was the proper Lunar Month of the Ancients, and at the fame time fhews the Reafon, why in the Luni-folar Year, the Months confifted of twenty-nine

and

and thirty Days alternately. For in the Month of twentynine Days, the Appendage of twelve Hours being omitted, was to be added to the next Synodic Revolution; which confifting likewise of twenty-nine Days twelve Hours, did with the twelve Hours omitted in the former Month, make up an exact Space of thirty Days. And this alternate Diftribution of Months, muft we fee happen conftantly and regularly.

What has been faid will be fufficient to give an Idea of the Aftronomical Month, in Ufe chiefly among the Ancients, and here explained, to pave the Way to what may be afterwards faid of their Chronology. As for the Civil Month, it is no more than that Space of Time, by which we divide a Year into twelve Parts, and is different in different Nations. The Civil Calendar Months which now obtain thro' Europe, confift of all thirty or thirty-one Days, February excepted, which every fourth Year includes twenty-nine Days, and the other Years only twenty-eight; but of this more hereafter.

We come now to the laft and greatest Distribution of Time founded on the Motion of the Heavenly Bodies; I mean that taken from the Sun's apparent Revolution in the Ecliptic, and called a Year. I fhall not enter into the nice Diftinctions of Aftronomers, who divide the Year into Sidereal and Tropical, as that would add but little to your Chronological Knowledge. It will better anfwer my Purpofe, to give a thort Hiftory of the Year, with its various Changes, and prefent Form. Befides the more obvious Revolution of the Sun, by which he is carried round the Earth in the Space of twenty-four Hours, and marks out the Quantity of a Natural Day; there is alfo a fecond Motion belonging to him, carried on more flowly, and not compleated till after fome confiderable Time. This is what Aftronomers call his annual Revolution, by which fetting out from fome remarkable Part of the Heavens, as the Equinoctial or Solstitial Points, he is obferved after a certain Number of Days, to return again to the fame, and fo on in continual Succeffion. Now as in the Cafe of the diurnal Motion, his regular Appearance and Difappearance, naturally drew after it the Obfervation of Mankind, and directed them to the cafy and convenient Diftinction of Time into Days: fo here, his annual Motion being attended with a Viciffitude of Seafons, which follow one another in Succeffion, and always return, when the Sun returns to the fame Part of his Orbit which produced them before; it would not be long before Men would become fenfible of these Alterations, and obferving them to be uniform and conftant, would by a Curiofity natural to them, be for finding

out