art of making or constructing dials; called also dialling, horolography, gnomonics, icatherica, photofictherica, &c.

Horologium, ὁρολόγιον, (composed of ὁράω, hora, "time, hour," and λόγος, "speech, discourse.") A common name among ancient writers for any instrument or machine for measuring the hours; (see Chronometer.)—Such are our clocks, watches, sun-dials, &c. See Clock, Watch, Dial, and Clepsydra.

Modern inventions, and gradual improvements, have given birth to some new terms that come properly under this head, and annexed new meanings to others totally different from what they had originally. All chronometers that announced the hour by striking on a bell, were called clocks; thus, we read of pocket-clocks, though nothing could seem more absurd than to suppose that a clock, according to the modern idea, should be carried in the pocket. In like manner, all clocks that did not strike the hour were called watches or time-pieces; and the different parts of a striking clock were distinguished by the watch-part and the clock-part; the former meaning that part which measures the time, and the latter the part which proclaims the hours. In the report of Sir Isaac Newton to the house of commons, anno 1713, relative to the longitude act, he states the difficulties of ascertaining the longitude by means of a watch: yet it is obvious, from several circumstances, that his remarks were directly to be understood of a time-piece regulated by a pendulum; for his objections are founded on the known properties of the pendulum, some of which differ essentially from the properties of the balance and spring. It is also to be remembered, that all the attempts of Huygens for finding the longitude were by means of pendulum clocks that did not strike the hour, and consequently, according to the language of the times, were called watches. At this time such machines for measuring time as are fixed in their place are called clocks, if they strike the hour; if they do not strike the hour, they are called time-pieces; and when constructed with more care, for a more accurate measure of time, they are... HOROPTER are called regulators. Some artists of late have affected to call such watches as were constructed for astronomical and nautical observations by the name of time-pieces, probably to intimate that they possess the advantages of those constructed with a pendulum.

Mr John Harrison first gave the name of time-keeper to his watch, for the performance of which he received from parliament the sum of £2,000l. See LONGITUDE.

For the account of the principles of this machine, see TIME-KEEPER. And for the chief improvements that have been made for the more accurate measure of time, see PALLETS, PENDULUM, and SCAPEMENT.