The Clepsydra is so named because the water escapes from it as it were by stealth, but in a regulated flow so as to permit of the lapse of time being computed thereby, even as by sand running through sand-glasses. The Clepsydra appears to have been at first used to limit the time during which persons were allowed to speak in the Athenian Courts of Justice; 'the first water,' says Æschines, 'being given to the accuser, the second to the accused, and the third to the judges,'—a special officer being 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 water allowed, depended upon the importance of the case. This custom, says Phavorinus, was to prevent babbling, that such as spake should be brief in their speeches. Ctesibius of Alexandria, who lived about 245, invented a much improved water-clock, mentioned by Vitruvius and Athenæus. Another kind of Clepsydra consisted of a vessel of water having a hole in it through which the fluid gradually escaped; a miniature boat floated upon the water and descended as the water decreased, whilst an oar placed in the boat indicated the hour by pointing to certain line-marks on the side of the vessel. The hole through which the water dropped was made, we are told, through a pearl, because it was supposed that the action of the water upon the pearl would not, as upon other substances, enlarge the aperture, nor would the pearl, it was imagined, be choked by the adhesion of any other material. The chief fault of the Clepsydra as a chronometer arose from the inequality of the flow of water, it being found to escape more rapidly when the vessel was full than when it was becoming empty, and also more speedily in hot weather than in cold. The Egyptians are however said to have measured by this machine the course of the sun; by it Tycho-Brahe computed the motion of the stars; and by it Dudley made his maritime observations. Plato furnished the original idea of the hydraulic organ by inventing a Clepsydra, or water-clock, which played upon flutes the hours of the night when darkness precluded their being shown by the index. Clepsydræ are still used in India.
The Sand-glass, as we have said, is an instrument of the same character as the Clepsydra,—the one measuring time by the fall of water and the other by the running of sand. Sand-glasses are known to have been used 200 B.C. The best hour-glasses, it is said, were those in which powdered egg-shells well dried in the oven were used instead of sand, such powder being less affected by changes in the atmosphere than sand would be. Sand-glasses are now seldom used except on board ship, and by domestics to compute the time for the boiling of eggs.
King Alfred's invention for measuring time by the burning of candles, which were marked by circular lines to show the progress of the hours, was another effort of rude skill, which however could have been but partially successful even in the opinion of its inventor, for the accuracy of candle-horologes is interfered with by many different influences, prominent among which must of course have been the varying qualities of the materials used in their manufacture, and the more or less care with which they were guarded from the wind, so as to prevent their guttering.
We now come to consider the date of the next grand step in the progress of Horology,—namely, that of the invention of the clock. The name itself may be derived either from the French, la cloche, a bell, or from the German, die gloke, or die kloke. There is no doubt that the word cloche was meant to distinguish the instrument which marked the hours by sounding a bell, from the montre or watch, which (derived from the Latin monstro, to show) merely shows the time by its hands. In ancient books the word cloche simply stands for a bell,—the monks being accustomed to ring a bell at certain periods marked for them by their sun-dials or hour-glasses, and 'What's o'clock?' in old writers is often merely equivalent to the inquiry, 'What hour was last struck by bell?' The word horologe or hour-measurer of course equally applied to the sun-dial, the clepsydra, and the clock, and this convertibility of terms makes it all the more difficult to trace the point at which the newer invention began. Beckmann, in an ingenious analysis of various statements as to the first inventors of clocks made to go by weights and wheels, ascribes the invention to the eleventh century, but he does not attempt to name the first clockmaker. His authority for the date is the life of William Abbot of Hirshan, wherein there is mention made of a machine used by the monks for measuring time, which cannot in Beckmann's opinion have been a clepsydra. Beckmann does not believe that clocks were of European origin, but that they were derived from the Saracens. He founds his opinion upon a horologe described by Trithenius which was presented by the Sultan of Egypt in 1232, to the Emperor Frederic II. of Germany. 'In the same year,' says he, 'the Saladin of Egypt sent by his ambassadors, as a gift to Frederic II., a valuable machine of wonderful construction, worth more than 5000 ducats. For it appeared to resemble internally a celestial globe in which figures of the sun, moon, and other planets, formed with the greatest skill, moved, being impelled by weights and wheels, so that performing their course in certain and fixed intervals, they pointed out the hour, night and day, with infallible certainty; also the twelve signs of the Zodiac with appropriate characters, moved with the firmament, contained within themselves the course of the planet.'
To whom the high honour belongs of inventing the clock is, to use a not unknown phrase, 'lost in the mists of antiquity.' All the ancients who were reported as skilful in mechanics seem to have obtained a modicum of credit as clock-inventors. Archimedes and Posidonius before, the Christian era, Boëthius in the 5th century, Pacificus about the middle of the 9th, Gerbert at the end of the 10th, Wallingford near the beginning of the 14th, and Dondi at the end of the 14th, have each in their turn been asserted to be the inventors of the clock.
The sphere of Archimedes, made 200 B.C., as mentioned by Claudian, was evidently an instrument with a maintaining power but without a regulator, and therefore would not measure time in any other manner than as a planetarium, turned by a handle, measures, or rather exhibits, the respective velocities of the heavenly bodies; and the same may be said of the sphere of Posidonius, as mentioned by Cicero ('De naturâ Deorum'). The clock of Boëthius was a clepsydra, as was also that of Pacificus, according to some, for Bailly in his History of Modern Astronomy asserts that Pacificus was the inventor of a clock going by means of a weight and a balance, and if so the invention must be ascribed to Pacificus; but Bailly gives no authority for his assertion. Gerbert's horologe is said to have been merely a sun-dial, and Wallingford's horologe, called the Albion, must have as much resembled a planetarium as a clock, for the motions of all the heavenly bodies appear to have been conducted by the maintaining power, whatever that was, without controlling mechanism. This instrument, made in 1326, is also described as having shown the ebb and flow of the sea, the hours, and the minutes.
There are, however, still earlier data as to clocks in England than this of Wallingford's, for we find that in 1288 a stone clock-tower was erected opposite Westminster Hall with a clock which cost 800 marks, the proceeds of a fine imposed upon Ralph de Hengham, Chief Justice of the Queen's Bench. The tower mentioned was still standing in 1715, and in it was a clock which struck the great bell known as Tom of Westminster so as to be heard by the people in all the law courts. In Queen Elizabeth's time the clock was changed for a dial upon the clock tower, which, however, bore upon its face the same Virgilian motto, 'Discite justitiam moniti,'—referring to the fine inflicted upon the Chief Justice for making an alteration in a record by which a poor dependent was made to pay 13s. 4d. instead of 6s. 8d. A dial with this motto was still to be seen in Palace Yard, Westminster, within the last dozen years, but was removed with the houses which were then demolished to make way for the gilded palings which have since been erected between Palace Yard and Bridge Street, Westminster.
In 1292 a clock was placed in Canterbury Cathedral, which, according to a statement in a Cottonian MS., cost £30, a large sum at that time.
Dante, who died in 1321, aged 57, makes the earliest mention of an orologio which struck the hour:
'Indi come orologio che ne chiami Nel hora che la sposa, d'Idio surge Amattinar lo sposo, perche l'ami.'