in astronomy, the time taken up by a star or planet in making a revolution round the sun; or the duration of its course till it return to the same part of its orbit.

The periodical times of the planets round the sun are as follow:

| Planet | Seconds | Min. | Hrs. | Days | |----------|---------|------|------|------| | Mercury | 87 | 23 | 15 | 53 | | Venus | 224 | 16 | 49 | 24 | | The earth| 365 | 6 | 9 | 14 | | Mars | 686 | 23 | 27 | 30 | | Jupiter | 4332 | 12 | 20 | 25 | | Saturn | 10759 | 6 | 36 | 26 |

There is a wonderful harmony between the distances of the planets from the sun, and their periods round him; the great law whereof is, that the squares of the periodical times of the primary planet, are to each other as the cubes of their distances from the sun: and likewise, the squares of the periodical times of the secondaries of any planet are to each other as the cubes of their distances from that primary. This harmony among the planets is one of the greatest confirmations of the Copernican hypothesis. See Astronomy, n° 132.

For the periods of the moon, see Astronomy, n° 223.

The periods of several comets are now pretty well ascertained. See Astronomy, n° 46 et seq.

chronology, denotes a revolution of a certain number of years, or a series of years, whereby, in different nations, and on different occasions, time is measured; such are the following.

Calippic Period, a system of seventy-six years. See Calippic.

Dionysian Period, or Victorian Period, a system of 532 lunar-solar and Julian years; which being elapsed, the characters of the moon fall again upon the same day and feria, and revolve in the same order, according to the opinion of the ancients.

This period is otherwise called the great paschal cycle, because the Christian church first used it to find the true time of the pascha or Easter. The sum of these years arise by multiplying together the cycles of the sun and moon. See Astronomy, n° 308.

Hipparchus's Period, a system of 304 years, both lunar and solar; which being elapsed, Hipparchus thought that the reckoning by the lunar motion would coincide again with the solar measures. This period comprehends 3760 lunar months, or 111,039 days; the sum of which arises from the multiplication of the Calippic period by 4, subtracting unity from the product.

Julian Period. See Julian.

grammar, denotes a small compass of discourse, containing a perfect sentence, and distinguished at the end by a point, or full stop, thus (.); and in members or divisions marked by commas, colons, &c.

oratory, See there, n° 44.

Calippic Period, a system of seventy-six years. See Calippic.

Dionysian Period, or Victorian Period, a system of 532 lunar-solar and Julian years; which being elapsed, the characters of the moon fall again upon the same day and feria, and revolve in the same order, according to the opinion of the ancients.

This period is otherwise called the great paschal cycle, because the Christian church first used it to find the true time of the pascha or Easter. The sum of these years arise by multiplying together the cycles of the sun and moon. See Astronomy, n° 308.

Hipparchus's Period, a system of 304 years, both lunar and solar; which being elapsed, Hipparchus thought that the reckoning by the lunar motion would coincide again with the solar measures. This period comprehends 3760 lunar months, or 111,039 days; the sum of which arises from the multiplication of the Calippic period by 4, subtracting unity from the product.

Julian Period. See Julian.

Period, in grammar, denotes a small compass of discourse, containing a perfect sentence, and distinguished at the end by a point, or full stop, thus (.); and in members or divisions marked by commas, colons, &c.

Period, in oratory, See there, n° 44.

Periodic, or Periodical, something that terminates and comprehends a period; such is a periodic month; being the space of time wherein the moon dispatches her period.