according to the most natural and obvious sense of the word, signifies that space of time during which it continues to be light; in contradistinction to night, which is that portion of time wherein it is dark: but the space of time in which it is light, being somewhat vague and indeterminate, the time between the rising and the setting of the sun is usually looked on as the day; and the time which lapses from its setting to its rising again, the night.

The word day is often taken in a large sense, so as to include the night also; or to denote the time of a whole apparent revolution of the sun round the earth; in which sense it is called by some a natural day, and by others an artificial one: but, to avoid confusion, it is usual to call it in the former sense simply the day, and in the latter a nycthemeron: by which term that acceptation of it is aptly denoted, as it implies both day and night. The nycthemeron is divided into twenty-four parts, called hours; which are of two sorts, equal, and unequal or temporary. See the article Hour.

Different nations begin their day at a different hour. Thus the Egyptians begin their day at midnight; from whom Hippocrates introduced that way of reckoning into astronomy, and Copernicus and others have followed him; but the greatest part of astronomers reckon the day to begin at noon, and so count twenty-four hours, till the noon of the next day; and not twice twelve, according to the vulgar computation. The method of beginning the day at midnight prevails in Britain, France, Spain, and most parts of Europe.

The Babylonians began their day at sunrise; reckoning the hour immediately before its rising again, the twenty-fourth hour of the day; from whence the hours reckoned in this way are called the Babylonian. In several parts of Germany, they begin their day at sunsetting, and reckon on till it sets next day, calling that the twenty-fourth hour; these are generally termed Italian hours. The Jews also began their nycthemeron at sunsetting; but then they divided it into twice twelve hours as we do; reckoning twelve for the day, be it long or short, and twelve for the night; so that their hours continually varying with the day and night, the hours of the day were longer than those of the night for one half year, and the contrary the other; from whence their hours are called temporary: those at the time of the equinoxes became equal, because then those of the day and night are so. The Romans also reckoned their hours after this manner, as do the Turks at this day.

This kind of hours is called planetary, because the seven planets were anciently looked upon as presiding over the affairs of the world, and to take it by turns each of these hours, according to the following order; Saturn first, then Jupiter, Mars, the Sun, Venus, Mercury, and last of all the Moon: hence they denominated each day of the week from that planet whose turn it was to preside the first hour of the nycthemeron. Thus, assigning the first hour of Saturday to Saturn, the second will fall to Jupiter, the third to Mars, and so the twenty-second of the same nycthemeron will fall to Saturn again, and therefore the twenty-third to Jupiter, and the last to Mars: so that on the first hour of the next day, it will fall to the sun to preside; and by the like manner of reckoning, the first hour of the next will fall to the Moon; of the next to Mars; of the next to Mercury; of the next to Jupiter; and of the next to Venus: hence the days of the week came to be distinguished by the Latin names of Dies Saturni, Solis, Lunae, Martis, Mercurii, Jovis, and Veneris; and among us, by the names of Saturday, Sunday, Monday, &c.

Day-Coal, in Natural History, a name given by the miners of England, and the common people who live in coal countries, to that seam or stratum of the coal which lies uppermost in the earth. The same vein or stratum of coal usually runs a great way through the country, and dips and rises in the earth at different places; so that this upper stratum, or day-coal, is in the various parts of the same stratum, sometimes near the surface, and sometimes many fathoms deep. The subterranean fires found in some of our coal countries feed principally on this coal; and are nearer to or farther from the surface as it rises or sinks.

Day-Fly. See Ephemeris, Entomology Index.

Day-Net, among fowlers. See Net.

Days of Grace, are those granted by the court at the prayer of the defendant or plaintiff, in whose delay it is.

Days of Grace, in commerce, are a customary number of days allowed for the payment of a bill of exchange, &c., after the same becomes due.

Three days of grace are allowed in Britain; ten in France and Danzig; eight at Naples; six at Venice, Amsterdam, Rotterdam, and Antwerp; four at Frankfurt; five at Leipzig; twelve at Hamburgh; six in Portugal; 14 in Spain; 30 in Genoa, &c.

In Britain the days of grace are given and taken as a matter of course, the bill being only paid on the last day; but in other countries, where the time is much longer, it would be reckoned dishonourable for a merchant to take advantage of it; bills are therefore paid on the very day they fall due.

Day's-Man, in the north of England, an arbitrator or person chosen to determine an affair in dispute.

Intercalary Days. See Intercalary Days.

Day's-Work, among seamen, the reckoning or account of the ship's course during 24 hours, or between noon and noon, according to the rules of trigonometry. See Dead-Reckoning.