The Development of the Water Clock (or clepsydra)
NOW we must take another backward step of thousands of years. In considering
the subject of time-recording, it seems necessary to wear a pair of mental
seven-league boots, for we must often pass back and forth over great periods
at single strides. While men were still improving the sun-dial, its
disadvantages were already recognized and search was being made for some
other means of telling time.
Suppose, for example, that one had only a sun-dial about the house; how
would one be able to tell time after sunset or on a dark day? How would one
know the hour if he were surrounded by tall buildings or a thick growth of
trees? And it might be very necessary to tell time under any of these
Then, again, merely as a question of accuracy, the sundial was not always
reliable. It would get badly out of the way if used by travelers, since
different markings were needed for different latitudes. While on shipboard
the motion of the waves would cause the shadow to swing around in the most
bewildering manner. Even under ideal conditions it was never absolutely
exact, because the apparent motion of our steady-gaited old sun is not quite
as dependable as most of us imagine.
Astronomers find that they must allow for what they call "equation of time"
in order to make their calculations come out true. The question need not be
discussed at this point, but it can be seen that, as humanity left its
earliest care-free days and began to get busy, and hurried and anxious over
its affairs, it came to feel that after all the sun-dial was not altogether
sufficient for its needs.
For this reason we are now taking a third big backward step, returning, this
time, not to the caveman but to ancient Babylon and Egypt, probably not less
than twenty-seven hundred years ago and possibly much longer. In this way we
meet the clepsydra.
The clepsydra was an interesting instrument, and it had an interesting name,
which meant the "thief of water" and came from two Greek words meaning
"thief" and "water"; you can trace this in our words "kleptomaniac" and
"hydrant." We shall now examine a timepiece that was much more nearly a
machine than was the simple shade-casting sun-dial.
The original idea was simple enough. At first, it was merely that of a
vessel of water, having a small hole in the bottom, so that the liquid
dripped out drop by drop. As the level within the jar was lowered, it showed
the time upon a scale. Thus, if the hole were so small and the vessel were
so large that it would require twenty-four hours for the water to drip away
at an absolutely steady rate, it may be seen that the side of the vessel
might easily have been marked with twenty-four divisions to indicate the
hours. It may also be seen that the water would drip as rapidly at night or
in shadow as in sunlight. And the clepsydra could be used indoors, which the
sun-dial could not, although it required attention in that it must be
regularly refilled and the orifice must always be kept completely open,
because the slightest stoppage would retard the rate of dripping and the
"clock" would run slow.
The sun, which, with the other heavenly bodies, had therefore been the sole
reliance of the human race in its time-reckoning could now be ignored and
the would-be timekeeper called to his aid another mighty servant from the
forces of nature--that of gravitation.
The most interesting human fact, however, about the clepsydra is that it
involved an entirely different conception of the marking of time. Now it was
not so much a question of when as of how long. A good sun-dial set in a
proper position would always indicate three o'clock when it was three
o'clock, but the clepsydra might do no such thing. It would merely show how
many hours had elapsed since last it was filled, and the steady drip, drip,
drip of the escaping water could--and did--lower the surface quite as evenly
at one time of day as at another.
We have already seen that the first purpose in marking time was merely for
making appointments, but the clepsydra shows that, with its invention,
mankind had already made some progress toward a new point of view. One
important factor in this change was the very practical need of telling time
at night, in stormy weather, or indoors, where the sun-dial could not be
used. The clepsydra, on the other hand, worked equally well at any hour or
place, and in all sorts of weather.
Nevertheless, it, too, proved to have certain faults. After a time, people
noticed the interesting fact that water ran faster from a full vessel than
from one which was nearly empty; this was, of course, because of the greater
pressure. Since such a variation interfered with calculations, they hit upon
the idea of a double vessel; the larger one below containing a float which
rose as the vessel filled, thus marking the hours upon the scale, and the
smaller one above, the one from which the water dripped, being kept
constantly filled to the point of overflow.
This improved form of clepsydra opened a field of fascinating possibilities
in time-recording--it gave the chance to make use of a machine. There is,
perhaps, no more interesting point in studying human development than to see
the steady, inevitable way in which mankind from its cave dwelling days has
tended machinery. Roughly, this progress may be characterized as of three
First. Primitive man--an upright-standing animal, naked, unarmed, weak as
compared with some creatures, slow as compared with others, clumsy as
compared with still others--a creature with many physical disadvantages, but
with the best brain in the animal kingdom.
Second. The tool-using man, who had begun to grasp weapons and to fashion
implements, thus supplementing his natural abilities by artificial means.
Third. The machine-making man, who has fashioned to himself a mechanical
"body" of incredible powers--that is to say, he has learned to intensify his
own powers through artificial means which he has invented, as when he made
the telescope to give himself greater vision; he has made inventions by
means of which he can outrun the antelopes, outfly the birds, outswim the
fishes, outgaze the eagles, and overmatch the elephants in sheer physical
force--he can turn night into day, can send his voice across the continent,
can strike crushing blows at a distance of many miles and can carry the
movements of the stars in his pocket. Some phases of this third stage were
foreshadowed when man first applied wheels and pulleys to his clepsydra.
Here, then, was water steadily raised or lowered by means of uniform
dropping; here was a float whose motion was controlled by that of the water;
here, in fact, was water-power with a means for applying it. Attach a cord
to the float, cause it to turn a wheel by use of the pulley-principle, and
the motion of the wheel would indicate the time. Still better, rig up a
turning-pointer, increase its speed through the use of toothed gear-wheels,
place it in front of a stationary disk divided to indicate the hours, and
now the apparatus looked not unlike a modern clock. Or attach a bell and let
it be caused to ring at a certain point in the motion-what was that but an
alarm-clock? Ctesibus of Alexandra was the one who is believed first to have
applied the toothed wheels to the clepsydra and this was about 140 B. C.
Clepsydrae were expensive of course; accurate mechanical work was never
cheap until modern times. Cunning craftsmen spent their time upon costly
decorations, and these water-clocks became triumphs of the jeweler's art, a
gift for kings. Therefore, like the sun-dial, they drifted into Rome--that
vast maelstrom of the ancient world. Imagine a great walled city of low
flat-roofed buildings, with fronts and porches of great columns, a town
mostly of stone and much of it of marble, gleaming white under the bright
Italian sun, the streets thronged with men in tunics and togas and here and
there some person of importance driving by, standing erect in his chariot
drawn by four horses harnessed abreast. And statues everywhere, in the
streets and about the buildings and in cool courtyards and gardens among
green leaves. The ancients thought of sculpture as an outdoor thing, and
where we have one statue in the streets or public places of our cities, they
had a hundred. We treasure the remains of them as artistic wonders in our
museums, but they put them indoors and out as common ornaments, and lived
Presently we hear of the clepsydra being used in Roman law courts by command
of Pompey, to limit the time of speakers. "This," says one writer of the
day, "was to prevent babblings, that such as spoke ought to be brief in
their speeches." It is not difficult to picture some pompous and tiresome
togaed advocate, rolling out sonorous Latin syllables as he cites precedents
and builds up arguments, while an unseen dropping checks the time against
him, and to hear his indignant surprise-and the chuckles of his
auditors-when the relentless water-clock cuts him short in the middle of
some period. Martial, the Latin poet, referring to a tiresome speaker who
repeatedly moistened his throat from a glass of water during the lengthy
speech, suggested that it would be an equal relief to him and to his
audience, if he were to drink from the clepsydra. But Roman lawyers were not
guileless, and sometimes, so we are told, they tampered with the mechanical
regulation or else introduced muddy water, which would run out more slowly.
This suggests one of the difficulties of the clepsydra. Still more serious
was the fact that it would freeze on frosty nights. There were no Pearys
among the ancient Romans; polar exploration interested them not at all; but
they did spread their conquests into regions of colder weather--as when
Julius Caesar mentions using the clepsydra to regulate the length of the
night-watches in Britain. His keen mind noted by this means that the summer
nights in Britain were shorter than those at Rome, a fact now known to be
due to difference of latitude.
As late as the ninth century, a clepsydra was regarded as a princely gift.
It is said, that the good caliph, Harun-al-Raschid, beloved by all readers
of the "Arabian Nights," sent one of great beauty to Charlemagne, the
Emperor of the West. Its case was elaborate, and, at the stroke of each
hour, small doors opened to give passage to cavaliers. After the twelfth
hour these cavaliers retired into the case. The striking apparatus consisted
of small balls which dropped into a resounding basin underneath.
The clepsydra appears to have been used throughout the Middle Ages in some
European countries, and it lingered along in Italy and France down to the
close of the fifteenth century. Some of these water-clocks were plain tin
tubes; some were hollow cups, each with a tiny hole at the bottom, which
were placed in water and gradually filled and sank in a definite space of
When the clepsydra was introduced from Egypt into Greece, and later into
Rome, one was considered enough for each town and was set in the
market-place or some public square. It was carefully guarded by a civic
officer, who religiously filled it at stated times. The nobility of the town
and the wealthy people sent their servants to find out the exact time, while
the poorer inhabitants were informed occasionally by the sound of the horn
which was blown by the attendant of the clepsydra to denote the hour of
changing the guard. This was much in the spirit of the calls of the watchmen
in old England, and later in our New England, who were, in a way, walking
clocks that shouted "Eleven o'clock and all's well," or whatever might be
Allowing for the fact that the clepsydra was none too accurate at the best
and that its reservoir must occasionally be refilled, it can be seen that
this early form of timepiece, having played its part, was ready to step off
the stage when a more practical successor should arrive.
With one of its earliest successors we are familiar.