HOROLOGIUM (ὡρολόγιον) was the name of the various instruments by means of which the ancients measured the time of the day and night. The earliest and simplest horologia of which mention is made, were called πόλος and γνώμων. Herodotus (II.109) ascribes their invention to the Babylonians; Favorinus (ap. Diog. Laert. II.1.3; compare Suidas, s.v. Γνώμων and Ἀναξίμανδρος) to Anaximander; and Pliny (H. N. II.76) to his disciple Anaximenes. Herodotus mentions the πόλος and γνώμων as two distinct instruments. Both, however, divided the day into twelve equal parts, and were a kind of sun-dial. The γνώμων, which was also called στοιχεῖον, was the more simple of the two, and probably the more ancient. It consisted of a staff or pillar standing perpendicular, in a place exposed to the sun (σκιάθηρον), so that the length of its shadow might be easily ascertained. The shadow of the gnomon was measured by feet, which were probably marked on the place where the shadow fell (Hesych. s.v. Ἐπτάπους σκύα and δωδεκάποδος: Pollux, I.72). The gnomon is almost without exception mentioned in connection with the δεῖπνον or the bath;º and the time for the former was towards sunset, or at the time when the shadow of the gnomon measured ten or twelve feet (Aristoph. Eccles. 652, with the Schol.; Pollux, l.c.; Menander, ap. Athen. VI p243; Hesych. s.v. Δεκάπουν Στοιχεῖον.) The longest shadow of the gnomon, at sunrise and sunset, was generally 12 feet, but in some cases 24 feet, so that at the time of the δεῖπνον it was 20 feet (Eubulides, ap. Athen. I p8). The time for bathing was when the gnomon threw a shadow of six feet (Lucian, Cronos. c. 17, Somn. s. Gall. c. 9). In later times the name gnomon was applied to any kind of sun-dial, especially its finger, which threw the shadow, and thus pointed to the hour. Even the clepsydra is sometimes called gnomon (Athen. II p42).
The gnomon was evidently a very imperfect instrument, and it was impossible to divide the day into twelve equal spaces by it. This may be the reason that we find it only used for such purposes as are mentioned above. The πόλος or ἡλιοτρόπιον, on the other hand, seems to have been a more perfect kind of sun-dial; but it appears, nevertheless, not to have been much used, as it is but seldom mentioned (Aristoph. ap. Polluc. IX.5). It consisted of a basin (λεκάνις), in the middle of which the perpendicular staff or finger (γνώμων) was erected, and in it the twelve parts of the day were marked by lines (Alciphron, Epist. III.4; Lucian, Lexiph. c. 4).
Another kind of horologium was the clepsydra (κλεψύδρα). It derived its name from κλέπτειν and ὑδωρ, as in its original and simple form it consisted of a vessel with several little openings (τρυπήματα) at the bottom, through which the water contained in it escaped, as it were, by stealth. This instrument seems at first to have been used only for the purpose of measuring the time during which persons were allowed to speak in the courts of justice at Athens. The time of its invention or introduction is not known; but in the age of Aristophanes (see Acharn. 653, Vesp. 93 and 827) it appears to have been in common use. Its form and construction may be seen very clearly from a passage of Aristotle (Problem. XVI.8). The clepsydra was a hollow globe, probably somewhat flat at the top part, where it had a short neck (αὐλός), like that of a bottle, through which the water was poured into it. This opening might be closed by a lid or stopper (πῶμα), to prevent the water running out at the bottom. The clepsydra which Aristotle had in view was probably not of glass or of any transparent material, but of bronze or brass, so that it could not be seen in the clepsydra itself what quantity of water had escaped. As the time for speaking in the Athenian courts was thus measured by water, the orators frequently use the term ὑδωρ instead of the time allowed to them (ἐν τῶ ἐμῷ ὑδατι, Demosth. de Coron. p274; ἐὰν ἐγχωρῃ τὸ ὑδωρ, c. Leoch. p1094). Aeschines (c. Ctesiph. p587), when describing the order in which the several parties were allowed to speak, says that the first water was given to the accuser, the second to the accused, and the third to the judges. An especial officer (ὁ ἐφ’ ὑδωρ) was appointed in the courts for the purpose of watching the clepsydra, and stopping it when any documents were read, whereby the speaker was interrupted; and it is to this officer that Demosthenes (c. Steph. I. p1103) calls out: σὺ δὲ ἐπίλαβε τὸ ὑδωρ. The time, and consequently the quantity of water allowed to a speaker depended on the importance of the case; and we are informed that in a γραφὴ παραπρεσβείας the water allowed to each party amounted to eleven amphorae (Aeschin. de Fals. Leg. § 126), whereas in trials concerning the right of inheritance only one amphora was allowed (Demosth. c. Macart. p1502). Those actions in which the time was thus measured to the speakers are called by Pollux (VIII.113) δίκαι πρὸς ὑδωρ; others are termed δίκαι ἄνευ ὑδατος, and in these the speakers were not tied down to a certain space of time. The only instance of this kind of actions of which we know, is the γραφὴ κακώσεως (Harpocrat. s.v. κάκωσις).
The clepsydra used in the courts of justice however was, properly speaking, no horologium; but smaller ones, made of glass, and of the same simple structure, were undoubtedly used very early in families for the purposes of ordinary life, and for dividing the day into twelve equal parts. In these glass-clepsydrae the division into twelve parts must have been visible, either on the glass-globe itself, or in the basin into which the water flowed. These instruments, however, did not show the time quite correctly all the year round; first, because the water ran out of the clepsydra sometimes quicker and sometimes slower, according to the different temperature of the water (Athen. II p42; Plut. Quaest. Natur. c. 7); and secondly, because the length of the hours varied in the different seasons of the year. To remove the second of these defects the inside of the clepsydra was covered with a coat of wax during the shorter days, and when they became longer the wax was gradually taken away again (Aen. Tact. c. 22). Plato is said to have used a νυκτερινόν ὡρολόγιον in the shape of a large clepsydra, which indicated the hours of the night, and seems to have been of a complicated structure (Athen. IV p174). This instance shows that at an early period improvements were made on the old and simple clepsydra. But all these improvements were excelled by the ingenious invention of Ctesibius, a celebrated mathematician of Alexandria (about 135 B.C.). It is called ὡρολόγιον ὑδραυλικὸν, and is described by Vitruvius (IX.9; compare Athen. l.c.). Water was p616 made to drop upon wheels which were thereby turned. The regular movement of these wheels was communicated to a small statue, which, gradually rising, pointed with a little stick to the hours marked on a pillar which was attached to the mechanism. It indicated the hours regularly throughout the year, but still required to be often attended to and regulated. This complicated clepsydra seems never to have come into general use, and was probably only found in the houses of very wealthy persons.a The sun-dial or gnomon, and a simpler kind of clepsydra, on the other hand, were much used down to a very late period. The twelve parts of the day were not designated by the name ὥρα until the time of the Alexandrian astronomers, and even then the old and vague divisions, described in the article Dies, were preferred in the affairs of common life. At the time of the geographer Hipparchus, however (about 150 B.C.), it seems to have been very common to reckon by hours (Cf. Becker, Charikles, vol. II, p490, &c).
There is still existing, though in ruins, a horological building, which is one of the most interesting monuments at Athens. It is the structure formerly called the Tower of the Winds, but now known as the Horological Monument of Andronicus Cyrrhestes (see Dict. of Biog. s.v.). It is expressly called horologium by Varro (R.R. III.5 §17). This building is fully described by Vitruvius (I.6 §4), and the preceding woodcuts show its elevation and ground plan, as restored by Stuart (Antiq. of Athens, vol. I c. 3).
The structure is octagonal; with its faces to the points of the compass. On the N.E. and N.W. sides are distyle Corinthian porticoes, giving access to the interior; and to the south wall is affixed a sort of turret, forming three quarters of a circle, to contain the cistern which supplied water to the clepsydra in the interior. On the summit of the building was a bronze figure of a Triton, holding a wand in his hand; and this figure turned on a pivot, so that the wand always pointed above that side of the building which faced the wind then blowing. The directions of the several faces were indicated by figures of the eight winds on the frieze of the entablature. On the plain wall below the entablature of each face, lines are still visible, which, with the gnomons that stood out above them, formed a series of sun-dials. In the centre of the interior of the building was a clepsydra, the remains of which are still visible, and are shown on the plan, where the dark lines represent the channels for the water, which was supplied from the turret on the south, and escaped by the hole in the centre.
The first horologium with which the Romans became acquainted was a sun-dial (solarium, or horologium sciothericum), and was, according to some writers, brought to Rome by Papirius Cursor twelve years before the war with Pyrrhus, and placed before the temple of Quirinus (Plin. H. N. VII.60); others stated that it was brought to Rome at the time of the first Punic war, by the consul M. Valerius Messala, and erected on a column behind the Rostra. But this solarium being made for a different latitude did not show the time at Rome correctly. Ninety-nine years afterwards, the censor Q. Marcius Philippus erected by the side of the old solarium a new one, which was more carefully regulated according to the latitude of Rome. But as sun-dials, however perfect they might be, were useless when the sky was cloudy, P. Scipio Nasica, in his censorship, 159 B.C., established a public clepsydra, which indicated the hours both of day and night. This clepsydra was in aftertimes generally called solarium (Plin. H. N. VII.60; Censorin. de Die Nat. c. 23). The word hora for hour was introduced at Rome at the time when the Romans became acquainted with the Greek horologia, and was in this signification well known at the time of Plautus (PseudOl. V.2.10). After the time of Scipio Nasica several horologia, chiefly solaria, seem to have been erected in various public places at Rome. A magnificent horologium was erected by Augustus in the Campus Martius. It was a gnomon in the shape of an obelisk; but Pliny (H. N. XXXVI.10) complains that in the course of time it had become incorrect. Another horologium stood in the Circus Flaminius (Vitruv. IX.9.1). Sometimes solaria were attached to the front-side of temples and basilicae (Varro, de Ling. Lat. VI.4; Gruter, Inscript. VI.6). The old solarium which had been erected behind the Rostra seems to have existed on that p617 spot till a very late period, and it would seem that the place was called ad Solarium, so that Cicero uses this expression as synonymous with Rostra or Forum (pro Quinct. 18, ad Herenn. IV.10). Horologia of various descriptions seems also to have been commonly kept by private individuals (Cic. ad Fam. XVI.18); and at the time of the emperors, the wealthy Romans used to keep slaves whose special duty it was to announce the hours of the day to their masters (Juven. X.215; Mart. VIII.67; Petron. 26).
From the number of solaria which have been discovered in modern times in Italy, we must infer that they were very generally used among the ancients. The following woodcut represents one of the simplest horologia which have been discovered; it seems to bear great similarity to that, the invention of which Vitruvius ascribes to Berosus. It was discovered in 1741, on the hill of Tusculum, among the ruins of an ancient villa, and is described by Gio. Luca Zuzzeri, in a work entitled D'una antica villa scoperta sul dosso del Tusculo, e d'un antico orologio a sole, Venezia, 1746, and by G. H. Martini, in his Abhandlung von den Sonnenuhren der Alten, Leipzig, 1777, p49, &c.
The following woodcut shows the same solarium as restored by Zuzzeri.
The breadth as well as the height (A O, and P A) are •somewhat more than eight inches; and the length (A B) •a little more than sixteen inches. The surface (A O R B) is horizontal. S P Q T is the basis of the solarium, which, originally, was probably erected upon a pillar. Its side, A S T B, inclines somewhat towards the basis. This inclination was called ἔγκλιμα, or inclinatio solarii and enclima succisum (Vitruv. l.c.), and shows the latitude or polar altitude of the place for which the solarium was made. The angle of the enclima is about 40°43′, which coincides with the latitude of Tusculum.b In the body of the solarium is the almost spherical excavation, H K D M I F N, which forms a double hemicyclium (hemicyclium excavatum ex quadrato, Vitruv.). Within this excavation the eleven hour-lines are marked which pass through three semicircles, H L N, K E F, and D M J. The middle one, K E F, represents the equator, the two others the tropic lines of winter and summer. The curve representing the summer tropic is somewhat more than a semicircle, the other two curves somewhat smaller. The ten middle parts or hours in each of the three curves are all equal to one another; but the two extreme ones, though equal to each other, are by one-fourth smaller than the rest. In the middle, G, of the curve D K H N F I,º there is a little square hole, in which the gnomon or pointer must have been fixed, and a trace of it is still visible in the lead by means of which it was fixed. It must have stood in a perpendicular position upon the surface A B R O, and at a certain distance from the surface it must have turned in a right angle above the spheric excavation, so that its end (C) extended as far as the middle of the equator, as it is restored in the above woodcut. See the description of another solarium in G.H. Martini's Antiquorum Monimentorum Sylloge, p95, &c.
Clepsydrae were used by the Romans in their camps, chiefly for the purpose of measuring accurately the four vigiliae into which the night was divided (Caes. de Bell. Gall. V.31;º Veget. de Re Milit. III.8; Aen. Tact. c. 22).
The custom of using clepsydrae as a check upon the speakers in the courts of justice at Rome was introduced by a law of Cn. Pompeius, in his third consulship (Tacit. De clar. Orat. 38). Before that time the speakers had been under no restrictions, but spoke as long as they had deemed proper. At Rome, as at Athens, the time allowed to the speakers depended upon the importance of the case. Pliny (Epist. II.11) states that on one important occasion he spoke for nearly five hours, ten large clepsydrae having been granted to him by the judices, but the case was so important that four others were added (Compare Plin. Epist. VI.2; Martial, VI.35, VIII.7). Pompeius, in his law, is said to have limited the time during which the accuser was allowed to speak to two hours, while the accused was allowed three hours (Ascon. in Milon. p37, ed. Orelli). This, however, as is clear from the case of Pliny and others, was not observed on all occasions, and we must supposed that it was merely the intention of Pompeius to fix the proportion of the time to be allowed to each party, that is, that in all cases the accuser should only have two-thirds of the time allowed to the accused. This supposition is supported by a case mentioned by Pliny (Epist. IV.9), where, according to law (e lege) the accuser had six hours, while the accused had nine. An especial officer was at Rome as well as at Athens appointed to stop the clepsydra during the time when documents were read (Apul. Apolog. I. and II; compare Ernesti, de Solariis, in his Opuscul. Philolog. et Crit. pp21‑31; Becker, Gallus, vol. I p186, &c.).
b This is not true. Tusculum (the modern Frascati, a few miles E of Rome) is at latitude 41°49.
Checking what is at about 40°43′, I find Pompeii. There has obviously been some confusion here: either the sundial described by Zuzzeri somehow came from the then new excavations at Pompeii; or more likely, Dr Schmitz has conflated here two different reports on ancient sundials.
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