The science of the measurement of time. Portions of time are distinguished in the first chapter of Genesis. The term "from time to time" (I Chron. ix. 25) means from hour to hour, that is, a complete day, just as in the Talmud and in rabbinical literature denotes twenty-four hours, a full day. The phrase ("hours and minutes"; Ber. 3b) shows that is sometimes used to distinguish the hour. The Hebrew word is used in the Talmud to describe also a second, a moment. The Chaldaic equivalent for "hour" is (Dan. iv. 16, 30 [A. V. 19, 33]). Other Biblical expressions of time are ("noon"), ("midday"), ("high day"), and or ("midnight"). According to the Talmud, the night is divided into three or four parts ( = "watches"; Ber. 3a). Other subdivisions of the day are ("dawn") and ("twilight"). In the Midrash the hour is divided into quarters termed "hands" (Yalḳ., Gen. 76). A "hand" signifies a quarter of an hour, as the hands and feet are the four principal members of the body.

The length of the hour is not given in the Bible, but in the Talmud, as stated above, twenty-four hours constitute a day. The hours of the night begin with sunset; and twelve hours from this the twelve hours of the day begin. The third hour of the day corresponds to 9 A.M.; the sixth hour to noon; the ninth hour to 3 P.M.; and so on. It is very probable that the same division of hours prevailed in Biblical times. The apportioning of twelve hours each to the day and the night was doubtless due to the Babylonian astrologers or authorities on horoscopes, who thought that the twelve constellations (; Ber. 32b) represented the hours, each having a supernatural power over a certain hour of the day or the night.

The device of the circle known as the dial, divided into twelve equal segments with a rod in the center, was probably first invented to point out the constellations. "Whoever wishes to know, may take a straight-cut rod and set it up on the level [in the center] between twelve fingers [inches, spaces] and measure its shadow for twelve degrees" ("Baraita di-Shemuel ha-Ḳaṭan," iii. 11, Frankfort-on-the-Main, 1863). Shabbethai b. Abraham (tenth century) writes that a Gentile of Babylon taught him the art of measuring the rod-shadow described in the Baraita of Samuel (Zunz, "G. V." p. 98).


The first use of the sun-dial ( = "the shadow of the degrees"; Isa. xxxviii. 8) in Biblical times is generally credited to Ahaz, King of Judah (739 B.C.); and some authorities suppose that he imported it from Assyria when he visited Tiglathpileser at Damascus, where he also copied the architecture of the altar (II Kings xvi. 10). Probably Ahaz constructed the dial in connection with the "covert of the Sabbath" (ib. verse 18), explained by Rashi to be a shaded place which Ahaz had built in the court of the Temple for rest and recreation. See Dial. The Talmud, however, does not credit the dial to Ahaz personally, as it must have been in existence before him, and it is not mentioned in his lifetime.

The sun-dial is known in the Mishnah as the "hour-stone" (); and its style or gnomon is called (= "nail" or "wire"; 'Eduy. iii. 8). Maimonides (Commentary to 'Eduy. ad loc.) describes the contrivance as "a broad and level stone set in the ground, with a circular line drawn on it; a perpendicular style [in the center] is raised on a perpendicular projection, in length usually a little less than that of a quarter of the segment indicated on the stone. The shadow of the style at every hour is marked and numbered on the circle of the stone."

Sun-Dial as Described by Maimonides.(After a sketch by J. D. Eisenstein.)The Gold Candelabrum.

The Mishnah relates that Helen, the mother of Monobaz II., King of Adiabene, made a gold "nebrashta," which she caused to be placed in front of the entrance to the Temple (Yoma iii. 10). The Tosefta adds that at daybreak sparks were emitted by the nebrashta; and it was then known that it was time to say the "Shema'" (ib. ed. Zuckermandel, ii. 183; comp. Gem. Yoma 37b). The Temple was situated on the west side of Mt. Moriah, and the nebrashta at its entrance on the east side. The latter thus caught the first rays of the sun, and served the useful purpose of indicating to the multitude in front of the entrance the exact time of sunrise. There are two interpretations for "nebrashta": one amora defines it as a candelabrum; another as a "ḳonbeta" (Yer. Yoma iii. 41b; comp. Jastrow, "Dict." s.v. = "snuffers").

The sun-dial in its primitive state was a series of marks showing the position of the sun's shadow on at wall at various hours of the day. The Midrash, commenting on Abraham's visitors who predicted the birth of Isaac at the anniversary of "this existing hour" (; Gen. xviii. 10), states that the visitors made a scratch on the wall, and said "when the sun reaches this spot" (Pesiḳ. R. 6 [ed. Friedmann, p. 24b]). Regarding a similar phrase, "to-morrow about this time" ( = "at the same hour"; Ex. ix. 18), Zebedee b. Levi says Moses made a scratch on the wall and predicted the hailstorm "when the sun reached this spot on the following day" (Ex. R. xii. 3). Rabban Simeon b. Gamaliel says any one can detect the difference between the lunar and the solar year (354 and 365 days respectively) by marking the shadow of the sun at the time of the solstice in Tammuz (July) and watching when the sun reaches the same spot in the following year. He will find a gain of eleven days over the lunar year (Seder 'Olam iv., end; Gen. R. xxxiii. 10).

The Clepsydra.

While the sun-dial was used to indicate the hours of the day when the sun shone, the clepsydra, or water-clock, was designed to designate the hours in cloudy weather and at night. Its earliest use was probably limited to the indication of the exact time of midnight. The Talmud explains that Moses, because he feared that the astronomers of Pharaoh would err in their calculations and consider him unreliable, said the Lord would kill the first-born in Egypt "about" midnight (Ex. xi. 4), whereas the event happened exactly at midnight (ib. xii. 29; Ber. 4a).

A unique and artistic contrivance to indicate midnight is said to have been invented by King David. As told by R. Simeon Ḥasida, David had his harp hanging over his couch and adjusted to the north wind, which at midnight blew across the strings, thus playing the instrument automatically. The music awakened David, who immediately prepared to study the Law until the morning star appeared (Ber. 3b). This story is based on the passages: "At midnight I will rise to give thanks unto thee" (Ps. cxix. 62), and "Awake up, my glory; awake, psaltery and harp: I myself will awake early" (ib. lvii. 9 [A. V. 8]).

The clepsydra is mentioned in Mishnah and Talmud under various names, perhaps to distinguish different forms and designs, all, however, signifying one thing; namely, the slow escape—literally the stealing away—of the water, drop by drop, which is the meaning of "clepsydra" in Greek. The actual word occurs in Gen. R. xlix., § 12 in the form . The variety known as "arpakas" (= [misspelled ] = ἅρπαζ, ἅρπάγιρν = "harpax," or perhaps = πρόχους) was made both of metal and of glass (Kelim xiv. 8, xxx. 4). This device was so arranged that, when completely filled, the pressing of a finger on the top, making it air-tight, would stop the running of the water from the bottom (Gen. R. iv. 3). Another form, called "tiatorus" (διατόρος = ), was made of metal. R. Jose considered it a "receptacle" because its contents dropped out slowly (Kelim ii. 6).

Clepsydra as Described in the Zohar.(After a sketch by J. D. Eisenstein.)In the Zohar.

A third kind was called "araḳ" (). The version in 'Er. 104a, ,should be read (= "it is permitted to raise the plummet [διαβήτης = "weight" or "ball"] and to allow the water to drop from the clepsydra"). This kind was used in a sickroom to awaken the patient at certain intervals. According to another account, the constant dropping of the water had a soothing effect on the patient's nerves (ib.). A correct description of this form of clepsydra is given in the Zohar, where it is related that R. Abba, on his way from Tiberias, stopped at an inn in the village of Tarsus. Before retiring he asked the innkeeper whether he had a rooster that would awaken him exactly at midnight for "ḥazot." The innkeeper assured Abba that he had a better device; namely: "A scale, having on one side a weight, and on the other a jug filled with water which escapes drop by drop. Exactly at midnight the vessel becomes empty, causing the weight on the other side to fall and sound an alarm throughout the house, thus announcing the hour of midnight. We made this appliance for the old man who stays here and who arises regularly at midnight to study the Law" (Zohar, Lek Leka, p. 182, Wilna, 1882).

The clepsydra in its simplest form is traced by some historians to the Greeks (about 430 B.C.), and by others to the censor Scipio Nasico (595 B.C.).

The general term "horologe" for a timepiece is used in Talmud and Midrash with reference to the passage, "This month shall be unto you the beginning of months" (Ex. xii. 2). The Rabbis understood the word (= "unto you") as indicating a surrender of the right to fix the time of the calendar; and they illustrate the idea in the Midrash with a parable of the horologe () which was delivered by the king to his son who succeeded him. Similarly the Almighty delivered the key for regulating the time for the months and the festivals to Israel (Yer. R. H. i. 3; Pesiḳ. R. 15 [ed. Friedmann, p. 77a]). In medieval literature the clock is known as ("the hour-guide"); in modern Hebrew, as .

  • Hour-Glasses, in Jour. Archœological Association (London), 1848, iii. 301; 1856, xii. 265; 1873, xxix. 130;
  • The Dial of Ahaz, in Jour. of Sacred Literature, i. 406, ii. 163, London, 1855-56;
  • Wood, Curiosities of Clocks and Watches, p. 7, London, 1866;
  • The Dial of Ahaz, in Popular Astronomy, Dec., 1898, pp. 537-549.
S. J. D. E.
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