Months fall fhort of the Calendar Months; to that the Epad, which expreffes how much the Lunar Year falls fhort of the Solar or Calendar Year, muft be confidered as continually increafing; and therefore to find the new Moons which are the Beginnings of the Synodical Months; an Addition must be made to the Epact in every Month, and more and more as the Year advances; which additional Numbers are called the Menftrual. Epacts. Only nothing is to be added to the Epact in January, because the annual Epact, together with the Day of the Month, does then exprefs the true Age of the Moon: But as January has 31 Days, which is near 2 Days more than a Synodical Month, therefore the Beginning of the Lunar Month in February, will fall near 2 Days fooner than it did in January: Confequently 2 is the Menftrual Epact of February; and then as February has but 28 or at moft 29 Days, which may be accounted one Day lefs than a Synodical Month, the next Lunar Month will begin one Day later in March than it did in February; ConTequently the Menftrual Epact of March decreases inftead of increafing, and is but 1. If from thence you reckon the Lunar Months to confift of 30 Days and 29 interchangeably, the new Moons will fall fo much earlier in the following Months, than the new Moon did in January, as is expreffed by the Menftrual Epacts in the Canon, viz. 2 Days in April, 3 in May, &c. until they amount to 11 Days at the End of the Year, which are then added to the annual Epact.

* To find the Time of the Moon's coming to the South, and of High-Water at London Bridge.

Four times the Moon's Age, if by 5 you divide,

Gives the Hour of her Southing: Add 2 for the Tide +.

*The Reason of this Rule is, that as the Moon at the Change comes to the South with the Sun, or at 12 o'clock; and as there are 30 Days, nearly, from one new Moon to another, and 24 Hours in a Day; therefore she loses one Day with another 34 or of an Hour in the time of her Southing Now the Moon's Age, or Number of Days from the Change being multiplied by 4, the Froduct is fo many fifths of an Hour as fhe has loft, which divided by 5 is reduced to Hours, and the Remainder, if any, multiplied by 12 will be Minutes.

The Reafon of adding 2 Hours to the Time of the Moon's Southing, for High-Water at London Bridge, is because, though it is High-Water in the open Sea, under the Meridian of London, when the Moon is on that Meridian, yet the Tide takes about 2 Hours more in flowing up to London.

СНАР.

A

Of EPOCHAS or ERAS.

N Epocha or Æra is a fixed Point of Time, at or near to which some remarkable Event has happened, from whence a Series of Years is computed, as, from the Creation of the World, from the Deluge, from the Birth of Christ, &c.

As the Conftitution of Epochas is merely arbitrary, and not founded on any aftronomical Confiderations, different Nations have made Ufe of different Epochas, commonly taken from fome

re

markable Occurrence in their respective Hiftories. Thus the Romans computed their Years from the Building of Rome. The Greeks from the first Inftitution of the Olympic Games, which were celebrated at the Beginning of every fifth Year. Hence they computed their Years by Olympiads, each Olympiad containing four Years. The Turks and Arabians, and generally all that profefs the Mahometan Religion, use the Epocha of the Hegeira, which is computed from the Time of Mahomet's Flight from Mecca to Medina. L 2 The

The ancient Jews made Ufe of various Epochas, taken from remarkable Occurrences in their Hiftory, as from their Exodus or Departure from Egypt, from the Building of Solomon's Temple, from the Affyrian and Babylonian Captivities, &c. The modern Jews ufe, principally, the Epocha of the Creation. The Epocha of Chrift, or A. D. i. e. the Year of our Lord commencing from our Saviour's Nativity, is now chiefly used by Chriftians, at least throughout Europe; for the Abyffinian Christians are faid to use the Dioclefian Era, in all their Ecclefiaftical Computations; which is otherwife called the Era of the Martyrs, because of the great Number of Chriftians that fuffered Martyrdom in the Reign of the Emperor Dioclefian. The vulgar Chriftian Era, whofe Author was Dionyfius Exiguus, an Abbot of Rome, in the fixth Century, is allowed by the best Chronologers to begin four Years too late, or after the true Time of Chrift's Birth: Yet long Ufe has now fo eftablifhed it, that there is lefs Inconvenience in using it with that Error, than there would be in correcting it. Dionyfius dated his Æra from the Conception of Chrift, which he fuppofed to be on March 25th, which Method obtained in England until the Year 1752. But now the first of January is reckoned the Beginning of the

Year

Year in all the British Dominions, as well as by most other Nations of Europe.

Befides thefe great Epochas, as we may call them, it has been ufual to compute by leffer Epochas, commencing with the Beginning of the Reign of Emperors and Kings, and expiring at their Death. Thus the ancient Romans reckoned by the Years of the Reign of their Emperors; and thus in England the Anno Regni, which is computed from the Beginning of the King's Reign, is generally used in Acts of Parliament, and Law Inftruments.