DAY (O. Eng. dæg, Ger. Tag; according to the New English Dictionary, “in no way related to the Lat. dies”), in astronomy, the interval of time in which a revolution of the earth on its axis is performed. Days are distinguished as solar, sidereal or lunar, according as the revolution is taken relatively to the sun, the stars or the moon. The solar day is the fundamental unit of time, not only in daily life but in astronomical practice. In the latter case, being determined by observations of the sun, it is taken to begin with the passage of the mean sun over the meridian of the place, or at mean noon, while the civil day begins at midnight. A vigorous effort was made during the last fifteen years of the 19th century to bring the two uses into harmony by beginning the astronomical day at midnight. In some isolated cases this has been done; but the general consensus of astronomers has been against it, the day as used in astronomy being only a measure of time, and having no relation to the period of daily repose. The time when the day shall begin is purely a matter of convenience. The present practice being the dominant one from the time of Ptolemy until the present, it was felt that the confusion in the combination of past and present astronomical observations, and the doubts and difficulties in using the astronomical ephemerides, formed a decisive argument against any change.

The question of a possible variability in the length of the day is one of fundamental importance. One necessary effect of the tidal retardation of the earth’s rotation is gradually to increase this length. It is remarkable that the discussion of ancient eclipses of the moon, and their comparison with modern observations, show only a small and rather doubtful change, amounting perhaps to less than one-hundredth of a second per century. As this amount seems to be markedly less than that which would be expected from the cause in question, it is probable that some other cause tends to accelerate the earth’s rotation and so to shorten the day. The moon’s apparent mean motion in longitude seems also to indicate slow periodic changes in the earth’s rotation; but these are not confirmed by transits of Mercury, which ought also to indicate them. (See Moon and Tides.)  (S. N.) 

Legal Aspects.—In law, a day may be either a dies naturalis or natural day, or a dies artificialis or artificial day. A natural day includes all the twenty-four hours from midnight to midnight. Fractions of the day are disregarded to avoid dispute, though sometimes the law will consider fractions, as where it is necessary to show the first of two acts. In cases where action must be taken for preserving or asserting a right, a day would mean the natural day of twenty-four hours, but on the other hand, as in cases of survivorship, for testamentary or other purposes, it would suffice if a person survived for even the smallest portion of the last day necessary.

When a statute directs any act to be done within so many days, these words mean clear days, i.e. a number of perfect intervening days, not counting the terminal days: if the statute says nothing about Sunday, the days mentioned mean consecutive days and include Sundays. Under some statutes (e.g. the Parliamentary Elections Act 1868, the Corrupt and Illegal Practices Prevention Act 1883) Sundays and holidays are excluded in reckoning days, and consequently all the Sundays, &c., of a prescribed sequence of days would be eliminated. So also, by custom, the word “day” may be understood in some special sense. In bills of lading and charter parties, when “days” or “running days” are spoken of without qualification, they usually mean consecutive days, and Sundays and holidays are counted, but when there is some qualification, as where a charter party required a cargo “to be discharged in fourteen days,” “days” will mean working days. Working days, again, vary in different ports, and the custom of the port will decide in each case what are working days. In English charter parties, unless the contrary is expressed, Christmas day and other recognized holidays are included as working days. A weather working day, a term sometimes used in charter parties, means a day when work is not prevented by the weather, and unless so provided for, a day on which work was rendered impossible by bad weather would still be counted as a working day. Lay days, which are days given to the charterer in a charter party either to load or unload without paying for the use of the ship, are days of the week, not periods of twenty-four hours.

Days of Grace.—When a bill of exchange is not payable at sight or on demand, certain days (called days of grace, from being originally a gratuitous favour) are added to the time of payment as fixed by the bill, and the bill is then due and payable on the last day of grace. In the United Kingdom, by the Bills of Exchange Act 1882, three days are allowed as days of grace, but when the last day of grace falls on Sunday, Christmas day, Good Friday or a day appointed by royal proclamation as a public fast or thanksgiving day, the bill is due and payable on the preceding business day. If the last day of grace is a bank holiday (other than Christmas day or Good Friday), or when the last day of grace is a Sunday, and the second day of grace is a bank holiday, the bill is due and payable on the succeeding business day. Days of grace (dies non) are in existence practically among English-speaking peoples only. They were abolished by the French Code (Code de Commerce, Liv. i. tit. 8, art. 135), and by most, if not all, of the European codes since framed.

Civil Days.—An artificial or civil day is, to a certain extent, difficult to define; it “may be regarded as a convenient term to signify all the various kinds of ‘day’ known in legal proceedings other than the natural day” (Ency. English Law, tit. “Day”). The Jews, Chaldeans and Babylonians began the day at the rising of the sun; the Athenians at the fall; the Umbri in Italy began at midday; the Egyptians and Romans at midnight; and in England, the United States and most of the countries of Europe the Roman civil day still prevails, the day usually commencing as soon as the clock begins to strike 12 p.m. of the preceding day.

In England the period of the civil day may also vary under different statutes. In criminal law the day formerly commenced at sunrise and extended to sunset, but by the Larceny Act 1861 the day is that period between six in the morning and nine in the evening. The same period of time comprises a day under the Housing of the Working Classes Act 1885 and the Public Health (London) Act 1891, but under the Public Health (Scotland) Act 1897 “day” is the period between 9 a.m. and 6 p.m. By an act of 1845, regulating the labour of children in print-works, “day” is defined as from 6 a.m. to 10 p.m. Daytime, within which distress for rent must be made, is from sunrise to sunset (Tulton v. Darke, 1860, 2 L.T. 361). An obligation to pay money on a certain day is theoretically discharged if the money is paid before midnight of the day on which it falls due, but custom has so far modified this that the law requires reasonable hours to be observed. If, for instance, payment has to be made at a bank or place of business, it must be within business hours.

When an act of parliament is expressed to come into operation on a certain day, it is to be construed as coming into operation on the expiration of the previous day (Interpretation Act 1889, § 36; Statutes [Definition of Time] Act 1880).

Under the orders of the supreme court the word “day” has two meanings. For purposes of personal service of writs, it means any time of the day or night on week-days, but excludes the time from twelve midnight on Saturday till twelve midnight on Sunday. For purposes of service not required to be personal, it means before six o’clock on any week-day except Saturday, and before 2 p.m. on Saturday.

Closed Days, i.e. Sunday, Christmas day and Good Friday, are excluded from all fixtures of time less than six days: otherwise they are included, unless the last day of the time fixed falls on one of those days (R.S.C., O. lxiv.).

American Practice.—In the United States a day is the space of time between midnight and midnight. The law pays no regard to fractions of a day except to prevent injustice. A “day’s work” is by statute in New York fixed at eight hours for all employees except farm and domestic servants, and for employees on railroads at ten hours (Laws 1897, ch. 415). In the recording acts relating to real property, fractions of a day are of the utmost importance, and all deeds, mortgages and other instruments affecting the property, take precedence in the order in which they were filed for record. Days of grace are abolished in many of the seventeen states in which the Negotiable Instruments law has been enacted. Sundays and public holidays are usually excluded in computing time if they are the last day within which the act was to be done. General public holidays throughout the United States are Christmas, Thanksgiving (last Thursday in November) and Independence (July 4th) days and Washington’s birthday (February 22nd). The several states have also certain local public holidays. (See also Month; Time.)  (T. A. I.)