These are called ClepsydrÆ. Vitruvius, the Roman architect and mechanist, attributes the invention of the water-clock to Ctesibus of Alexandria, who flourished in the reign of Ptolemy Euergetes, about two hundred and forty-five years before the Christian era. The same author says, the machine was first introduced at Rome, two hundred and fifty seven years previous to the Christian era. There is reason to believe it was first introduced at Rome into courts of justice, from Greece, as it had been originally used in Greece for this purpose; the Roman orators being guided in the time they occupied the court, by this instrument, as we may learn from this expression of Cicero, “Latrare ad clepsydram.” Cicero also informs us, that it was first introduced into courts of justice, in the third consulate of Pompey.

It has been discovered that the inventions of Egypt, Chaldea, and other Oriental countries constantly travelled to Rome and the West. Long since the respective periods previously mentioned, has the honour of this invention been claimed by Burgundians, Bolognese, and other Italians; sometimes by Frenchmen, but chiefly by Germans.

Their claim for invention seems to be questionable in numerous instances, whatever it may be for improvement; they certainly cannot, consistently with what we have stated, be considered as the first inventors; although there is nothing to be alleged against these respective people being the discoverers of designs which had a previous existence unknown to them.

With equal or much more propriety might the Arabians, in point of time (could that be of consequence) be considered as inventors of this machine; and they are well known to possess the least claim to original invention of any people. They, however, have a merit, notwithstanding: but it is of a negative kind; for those arts, sciences, &c. which were (by chance) saved from the destruction of their bigoted ignorance, and which, when the fortune of war had thrown into their hands those pure designs of intellectual Greece, mere accident had wrested from their zealous fury. These they transmitted to a more ingenious people as pure as they had received them; but upon precisely as good grounds as the before-named Europeans claimed this original invention, might the Arabians have assumed that honour. For we read that Haroun al Raschid, Caliph of Bagdad, then the chief of the Saracen empire, sent as a present to Charlemagne, a clock of curious workmanship, which was put into motion by a clepsydra; which instrument is said, by Dr. Adams, “to have been used by the ancients to measure time by water running out of a vessel.”

It consists of a cylinder divided into small cells, and suspended by a thread fixed to its axis in a frame, on which the hour distances, found by trial, are marked out. As the water flows from one cell into another, it changes slowly the centre of gravity of the cylinder, and puts it in motion.

The form of this instrument is thus described by Dr. Beckmann:—

“The most common kinds of these water-clocks, however, correspond in this, that the water issued drop by drop through a hole of the vessel, and fell into another, in which a light body, that floated, marked the height of the water as it rose, and by these means the time that had elapsed.”

The most improved form the same instrument has acquired, is thus described, by the same author, from one in his own possession.

“Amongst the newest improvements added to this machine may be reckoned an alarum, which consists of a bell and small wheels, like that of a clock that strikes the hours, screwed to the top of the frame in which the cylinder is suspended. The axis of the cylinder, at the hour when one is desirous of being awakened, pushes down a small crank, which, by letting fall a weight, puts the alarum in motion. A dial plate with a handle is also placed over the frame.”

In respect to the invention of clepsydrÆ, we should think the original inventor took his first idea from the use of an instrument common in Egypt, which that people called a Canob, or Nilometer, being a large stone vessel of the shape of a sarcophagus, into which water was daily poured, by proper officers, during the increase of the Nile, to show the people whether they had a prospect of plenty, or were to expect a scarcity in the ensuing year. As the fall of the water, after it had risen to a due height, was of equal importance to them; so the water was suffered to run out proportionably to its decrease in the river, being ascertained by just and equal marks which they generally well understood.

Vitrum horae had also been invented to describe the progress of time. These were conical hour-glasses, in which were placed a portion of sand; the glasses were joined together at the apex of the cone, with a small aperture of communication between the two.—From the glass, in which the sand is deposited, it dropped, grain by grain, into the sand below, standing upon its flat basis. These machines are called hour-glasses, and well known. We have been unable to discover any account of the origin of this instrument; but, from its simplicity, it admits of no improvement. It is also believed this had its origin in a convent.