HOROLOGY (Gr. hors, a defined portion of time) is that branch of applied science that has for its object the measurement of time. Although it is easy to look back on a period when time, according to the modern conception of it, as measured by hours, and minutes, and seconds, was unknown, yet we find progress early made in the measure ment of larger periods of time, by observations of the heavenly bodies; and although, in the later progress of astronomy, it is found that the movements of the more conspicu ous heavenly bodies do not afford accurate marks for the equable measurement of time, they were, for practical objects, sufficient, and afforded at least a better measure of time than any other phenomena which came under the observation of mankind. Thus, time was early divided into years, according to the motion of the sun among the constella tions; into months, according to the motion of the moon relatively to the sun's place in the heavens; and into days, by the alternate light and darkness caused by the rising and setting of the sun. It was long, however, before any accurate measure was found for a division of the day itself. The earliest measure employed for this purpose that we can trace is the shadow of an upright object, which gave a rough measure of time by the variations in its length and position. This suggested the invention of sun-dials (see DIAL). Another means early adopted for the measurement of short periods of time was by the quantity of water discharged by dropping from one vessel into another.
Instruments for the measurement of time on this principle were called clepsydra; (q.v.).
The running of fine sand from one vessel into another was found to afford a still more certain measure, and hence the invention of the hour-glass (q.v.). King Alfred is said to have observed the lapse of time by noting the gradual shortening of a lighted candle It is not very easy to trace to its source the history of the invention to which the modern clock owes its parentage; the earliest, however, of which we have a complete description, and perhaps the earliest which attained any distinct superiority to the rude machines already mentioned, was the clock of Henry Vie or De Wyck, a German, erected in the tower of the palace of Charles V., king of France, in 1379. A sketch of this clock, which is subjoined, will be useful not only from its historical interest, but also because, from its tive simplicity, it will form a ground- work for further explanation of the mechanism of clocks and watches in their more complicated forms. It will be readily
stood, from a glance at the annexed figure, that as the weight A tends to uncoil the cord and set in motion the cylinder B round its axis, the motion will be successively communicated to the various toothed wheels in the figure, and finally to the crown-wheel or escapement-wheel, I; the teeth of which so act on the two small levers or lets, i, 7t, projecting from and forming part of the pended upright spindle or vertical axis, KM, on which is fixed the regulator or balance, LL, that an alternating or vibratory, instead of a circular, motion of the balance itself is the result. The hands of the clock are aNaelied to the wheel N, also set in motion by 1 _y Lie cylinder B. Now, unless there were some cheek upon the motion, it is manifest that the heavy weight A would go rapidly to the ground, causing the wheels to rotate, the balance to vibrate, and the hands to go round with increasing velocity. In order to. prevent this rapid unwinding of the clock-work, and adjust it to the more deliberate measurement of time, the balance is, in De Wyck's clock,loaded with two weights, m, m; and the further these are removed from the axis or spindle, KM, the more heavily they will resist and counter act the escapement of the levers, and the rapidity of the rotation of the escapement wheel, till the clock be brought to go neither too quick nor too slow.
The above construction is probably the basis of all the principal time-keeping machines in use in the 16th century. The great epoch in the history of horology is marked by the application to it of the pendulum (q.v.) as a regulating power. This was effected by Huygens (q.v.) about 1657. This philosopher, in adapting the pendulum to the machinery previously invented, had little more to do than simply to add a new wheel to the movement, so as to enable him to place the crown-wheel and spindle in a horizontal instead of a perpendicular position, that the lower arm of the balance— then of course perpendicular, instead of horizontal, as iu De Wyck's clock—might be extended, as it were, downwards, and thus, in fact, be converted into a pendulum.