HOUR, hora, in chronology, an aliquot part of a natural day, usually a twenty fourth, sometimes a twelfth. But the word hour has not always been of the same signification; for in ancient times an hour did indefinitely express a short space of time. It is thought too, that anciently the four seasons of the year, wherein the sun finishes its annual course, had the name of hours, because 'torus instituted a cer tain year, consisting of three months; and for this reason the ancients called spring, summer, autumn, and winter, hours, and the year itself hours : of which some foot steps appear in this, that the Greeks call ed their annals Hori ; and the writers of them horographi. However it be, the di vision of the day into hours is very an cient, though the most ancient hour is that of the twelfth part of the day.
An hour, with us, is a m easure or quan tity of time, equal to a twenty-fourth part of the natural day, or nychthemeron ; or it is the duration of the twenty-fourth part of the earth's diurnal rotation. Fif teen degrees of the equator answer to an hour ; though not precisely, yet near enough for common use.
The hour is divided into sixty minntes; the minute into sixty seconds ; the se. conds into sixty thirds, &c.
There are divers kinds of hours, used by chronologers, astronomers, dialists, &c. Sometimes hours are divided into equal and unequal. Equal hours are the twenty-fourth part of a day and night pre cisely ; that is, the time wherein fifteen degrees of the equator mount above the horizon. These are also called equinoc
tial hours, because they are measured on the equinoctial : and astronomical, be cause used by astronomers. They are also differently denominated, according to the manner of accounting them in dif ferent countries. Astronomical hours are equal hours, reckoned from noon, or mid-day, in a continued series of twenty four. Babylonish hours are equal hours, reckoned in the same manner from sun rise. ['he Italian hours are also equal hours, reckoned in the same manner too, from sun setting. European hours are also equal hours, reckoned from mid night ; twelve from thence too'noon, and twelve more from noon to mid-night Jewish, or planetary or ancient hours are the twelfth part of the artificial day and night, each being divided into twelve equal parts. Hence, as it is only in the time of the equinoxes that the artificial day is equal to the night, it is then only that the hours of the day are equal to those of the night : at other times they will be always either increasing or de creasing. And they will be the more or less unequal according to the obliquity of the sphere.
Nona a popular kind of chrono meter, which serves to measure the flux of time by the running of sand from one vessel into another. Glasses of this kind for half and quarter hours, and for less di visions of time, are much used at sea.