). A name given to 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
. Herodotus (ii. 109), who ascribes their invention to
the Babylonians, mentions the πόλος
as two distinct instruments. Both, however, divided the day into twelve
parts, and were a kind of sun
dial. The γνωμων
, 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
), 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 (Poll.i. 72
). The gnomon is
almost without exception mentioned in connection with the δεῖπνον
or the bath; and the time for the former was towards sunset, or at the
time when the shadow of the gnomon measured ten or twelve feet (Eccles.
with the Schol.; Poll. l. c.). The longest shadow of the gnomon, at sunrise and sunset, was
twelve feet. The time for bathing was when the gnomon threw a shadow of six feet (Lucian,
, c. 17; Somn. s. Gall.
c. 9). In later times the
name gnomon was applied to any kind of sundial, and especially to its finger, which threw the
shadow, and thus pointed to the hour. Even the clepsydra is sometimes called gnomon (Athen.
ii. p. 42).
The gnomon was evidently a very imperfect instrument, and it was impossible to divide the
day into twelve equal spaces by it. The πόλος
, on the other hand, seems to have been a more perfect
kind of sundial; but it appears, nevertheless, not to have been much used, as it is but seldom
mentioned (Aristoph. ap.
). It consisted of a basin (λεκανίς
), 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 (Lucian, Lexiph.
Another kind of horologium was the clepsydra
). It derived its name from κλέπτειν
, 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
692) 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
), 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 ὕδωρ
instead of the time
allowed to them (ἐν τῷ ἐμῷ ὕδατι
, Demosth. De Coron. p. 274.139
). Aeschines (c. Ctesiph. 197
), 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 ἐφ̓ ὕδωρ
) 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. The time, and consequently the quantity of water allowed to a speaker
depended upon the importance of the case; and we are informed that in a γραφὴ παραπρεσβείας
the water allowed to each party amounted to eleven amphorae
(De Fals. Leg.
126), whereas in trials concerning the right of inheritance
only one amphora was allowed (Demosth. c. Macart.
p. 1052.8). Those actions in
which the time was thus measured to the speakers are called by Pollux (viii. 113) δίκαι πρὸς ὕδωρ
: others are termed δίκαι
, and in these the speakers were not tied down to a certain space of
The clepsydra used in the courts of justice, however, was, properly speaking, not a
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 (Quaest. Nat.
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. 22.10). Plato is said to have used a νυκτερινὸν
in the shape of a large clepsydra, which indicated the hours of the
night, and seems to have been of a complicated structure. 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
(q.v.), a celebrated mathematician of Alexandria (about B.C. 135). It is called ὡρολόγιον ὑδραυλικόν
, and is described by Vitruvius (ix. 9). Water
was 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 found only
in the houses of very wealthy persons. The sundial 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
, were preferred in the affairs of common life. At
the time of the geographer Hipparchus, however (about B.C. 150), it seems to have been very
common to reckon by hours.
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. It is expressly
by Varro (R. R.
iii. 5.17). This
building is fully described by Vitruvius (i. 6.4), and the following illustration shows its
ground-plan. For the elevation see the article Andronicus
Ground-plan of the Horological Monument of Andronicus Cyrrhestes at Athens.
The structure is octagonal, with its faces to the points of the compass. On the northeast
and northwest sides are distyle Corinthian porticos, 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
sundials. 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. Three other Athenian horologia are extant, one in the monument of Thrasyllus, another
that of Phaedrus in the British Museum (C. I. G.
522), a third in the theatre
of Dionysus, besides others from different parts of Greece.
The first horologium with which the Romans became acquainted was the sundial (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 (Pliny , Pliny H.
N. vii. 213
). Varro stated that it was brought to Rome from Catina in Sicily,
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 sundials, however perfect they might be, were
useless when the sky was cloudy, P. Scipio Nasica, in his censorship, B.C. 159, established a
public clepsydra, which indicated the hours both of day and night. This clepsydra was in
after-times generally called solarium
(De N. D.
87). 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 (Pseud. 1307
). 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 (Pliny H.
N. xxxvi. 73
) complains that in the course of time it had become incorrect.
Horologia of various descriptions seem also to have been commonly kept by private individuals
xvi. 18, 3); 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
, with Mayor's note; Mart.viii.
; Petron. 26
From the number of solaria which have been discovered in modern times in Italy (thirteen
having been discovered in the neighbourhood of Rome alone), we must infer that they were very
generally used among the ancients. The following illustrations represent 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,
and is described by Zuzzeri (Venice, 1746)
, and by G. H. Martini, in his
Abhandlung von den Sonnenuhren der Alten
, p. 49 (Leipzig, 1777)
Horologium. (From Tusculum.)
The following illustration shows the same solarium as restored by Zuzzeri:
The same restored.
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. In the body of the solarium is the almost
spherical excavation (H K D M I F N), which forms a double hemicyclium. Within this excavation
the eleven hour-lines are marked which pass through three semicircles (H L N, K E F, and D M
I). 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 I I), 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 last illustration.
Clepsydrae were used by the Romans in their camps, chiefly for the purpose of measuring
accurately the four watches into which the night was divided (B. G.
The custom of using clepsydrae as a check upon the speakers in the courts of justice at Rome
is said to have been introduced by a law of Cn. Pompeius, in his third consulship (De
38), who adds, before that time the speakers had been under no
restrictions, but spoke as long as they deemed proper. But there is some inaccuracy here, as
Cicero in B.C. 70 (In Verr.
i. 9, 25) speaks of his legitimae
in B.C. 63 (Pro Rab. Perd.
2, 6) his defence is limited to half
an hour; and in B.C. 59 (Pro Flacc.
33, 82) six hours are allotted. At Rome, as
at Athens, the time allowed to the speakers depended upon the importance of the case. Pliny
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. (Cf. Pliny, Epist.
vi. 2.) The law of
Pompeius only limited the time during which the accuser was allowed to speak to two hours,
while the accused was allowed three hours in the case of prosecutions de
It is clear from the case of Pliny (Epist.
iv. 9) and others that
this restriction was not observed on all occasions. An especial officer was at Rome as well as
at Athens appointed to stop the clepsydra during the time when documents were read
i. and ii.). See Ernesti, De Solariis
, in his
Opuscul. Philolog. et Crit.
pp. 21-31; Wöpcke,
Disquisitiones Arch. Math. Circa Solaria Veterum (Berlin, 1842)
, ii. pp. 407 foll.; and especially Marquardt,
pp. 370 foll.