HORNPIPE. An animated sort of dance. HORN-STONE. A species of flint. HORNWORK (in Fortification.) An out work which advances towards the field. HOROLOGY. The science which treats ea the measuring of portions of time The principal instruments used in the measuring of time are dials, clepsydrn or water-clocks: clocks, watches, and in some cases also hour. glasses.
The dial was doubtless one of the first in struments contrived for the measuring of time by means of the sun. The first nu record is the dial of Ahaz mentioned in Isaiah. This kin began to reign 400 years before Alexan der, and within 12 years of the building of Rome. The Chaldee historian Berosus is said to have constructed a dial on a reclining plane almost parallel to the equator. Aristar ehes the S'meen, 'Males, and where, are also mentioned as the makers of dials. The first sun-dial at Rome was set np by Papirius Cur sor in the 460th year of the building of the cite. The subject of &tilling, or of making ails,' has particularly occupied the attention of or.thenvesels its within the last three centu ries. Chiles is the first professed writer on the subject Deschales and Ozanam in their Cour SeS, and Wolfing in his Elements, have'sim plified the science. AL Picard gave a new method of making large dials by calculating i the hour lines, and De In Hire, in his Dial ling, gave a geometrical method of drawing hour Imes from certain pouts determined by observation. The method of drawing pn mary dials on easy principles is to be found in the Dialling of Everhard Walper, and the Rudiments Mathematica of Sehtettian Man ner. Among the more modern treatises on
this subject may be reckoned that of Wells in his Art of Sha&ws, Ferguson in his Lectures on Mechanics, Emerson in his Dialling, Lead better in his Mechanic Dialling, Mr. W. Jones in his Instrumental Dialling, and Bishop Horsley in his Mathematical Tracts.
Scipio Nasica was the first who constructed the clepsydra, although it is supposed to have been invested by the Egyptians under the Ptolemies about 150 years before the Christian I era. They serve fur measuring time in the winter, as the sun-dials do in the summer but they had two great defects : the one, that the water ran out with greater or less facility, as the air was more or less dense; and other, that the water ran more readily at the beginning than towards the conclusion. Mel Egyptians, by this machine, measured the course of the sun ; and Tycho Brahe, in modem times, made use of it to measure the motion of the wars, dx. Dudley also used the same contrivance in making all his mari time observations.
The invention of clocks has been ascribed to different authors ; namely, to Boetius in the sixth century to Paciticus, Archdeacon of Verona, and to Silitster, in the tenth The art of measuring hours.