HOROLOGY. 



on the fronts and gables of many of our old man- 

 sions. At present, the most common construction 

 is the horizontal dial, or that in which the plane 

 of the dial-plate is parallel to the horizon. In this 

 form the style or gnomon G, 

 the edge of the shadow of 

 which determines the hour- 

 line, runs in the plane of the 

 meridian that is, due north 

 and south ; while its sloping 

 edge forms an angle with 

 the horizon, or plane of 

 the dial, equal to the lati- 

 tude of the place in which 

 the instrument is situated, 

 and hence parallel to the earth's axis. 



Although a sun-dial may certainly be adjusted 

 so as to point out the time of day within a few 

 minutes, it is needless here to dwell further on the 

 details of an instrument now of little use. The 

 most perfect of sun-dials being only available in 

 sunshine, and not at all through the night in 

 which, by the way, moon-dials were sometimes 

 used they were partly superseded, even at a very 

 remote period, by 



CLEPSYDRAE AND SAND-GLASSES. 



It has been thought that the regular motion of 

 the dropping of water, and the simpler forms of 

 clepsydrae, or water - clocks, were used for the 

 measurement of time even previous to the inven- 

 tion of sun-dials. They certainly were known in 

 very remote antiquity, and were then used in 

 various parts of Asia and Europe ; in China, 

 India, Chaldea, Egypt, Italy, and Greece ; into 

 the last of which countries they were introduced 

 by Plato. Julius Caesar found them even in 

 Britain. The Romans themselves had clepsydras 

 100 years before Caesar's invasion ; and it is sup- 

 posed that the Phcenicians had introduced them 

 into Britain through Cornwall, where they traded 

 for tin. The clepsydra invented by Ctesibius of 

 Alexandria, 250 B.C. consisted of a jar containing 

 water, which slowly escaped by a hole at the 

 bottom, while the oar of a miniature boat on the 

 surface, as it sank with the fall of the water, 

 pointed out the hours, which were marked on the 

 side of the jar. It is even alleged that toothed- 

 wheels were applied to clepsydrae by Ctesibius. 

 Such instruments, however, though brought to 

 great perfection in the ninth and tenth centuries, 

 and indeed still used in India, have never been 

 made to measure time with great accuracy. The 

 principal defect is the unequal dropping of the 

 water, caused by the varying depth or weight of 

 the liquid in the containing vessel, increase or 

 decrease of temperature, and change of barometric 

 pressure. As time-keepers, clepsydras may there- 

 fore be considered as superseded by ordinary 

 clocks and watches. 



The running of fine well-dried sand through a 

 tube, or from an orifice in a containing vessel, was 

 another obvious species of regular motion, very 

 analogous to the flowing or dropping of water. 

 Accordingly, sand-glasses, still in use in this and 

 other countries, were of very early invention. We 

 have evidence of their employment in the East 

 about a couple of centuries before the Christian 

 era. Though now used only for rude and trivial 

 purposes the half-minute glass being still em- 



ployed on shipboard, and the three-and-a-half 

 minute egg-glass by the housemaid some cen- 

 turies ago, in Western Europe, they were the 

 almost universal measurers of brief intervals ; and 

 hence the numerous allusions of our poets, and the 

 symbolical representations on our monuments and 

 sculptures. 



PLANETARIUMS OR ORRERIES. 



It is rather a curious circumstance, that, long 

 before the invention of clocks or watches, artificial 

 machines were constructed, imitative of the mo- 

 tions of the sun, moon, and planets the natural 

 time-keepers. 



Of the planetariums of modern times, the first 

 in England was one made for Lord Orrery, whose 

 name has since been given to such machines. 

 The talented and self-taught astronomer, Fergu- 

 son, who was originally a poor Scottish herd-boy, 

 made several orreries, and used chronometers to 

 keep them in motion. But though the accuracy 

 with which wheels and pinions can be made to 

 represent different revolutions is beautifully illus- 

 trated by the best of these machines, they can 

 give no just conception of the relative size, dis- 

 tance, or velocity of the planets, or hence of the 

 periods of their revolution. ' As to getting correct 

 notions on this subject (the magnitude and dis- 

 tances of the planets),' says Sir John Herschel, 

 ' by drawing circles on paper, or, still worse, from 

 those veiy childish toys called orreries, it is out of 

 the question.' A verdict so decided, and from 

 such a source, renders any attempt at description 

 or illustration unmeaning and superfluous. 



CLOCKS. 



The strong hold which the planetary motions 

 appear to have taken on the minds of our fore- 

 fathers, as the great antetypes of all true time- 

 keepers, is also curiously manifested in the fact, 

 that even when a more detailed measurement of 

 time became necessary, in the intellectual progress 

 of nations, these motions still continued to be repre- 

 sented, so that the first clock of which we have 

 any perfectly authentic account that, namely, in- 

 vented by Wallingford, abbot of St Albans, in 

 1326 not only shewed the hours, but the apparent 

 motion of the sun, the changes of the moon, the 

 ebb and flow of the tides, &c. This, however, was 

 by no means the first clock ever constructed ; 

 instruments with weights, wheels, pinions, and a 

 balance, for the measurement of time, having been 

 long previously known, though by whom invented, 

 appears to be a subject of much controversy. 

 Doubtless, they required more than the intellect 

 of a single mind. Be this as it may, the most 

 ancient clock of which we have any description is 

 that of Henry Vic or De Wyck, a German, erected 

 in the tower of the palace of Charles V. king of 

 France, in 1379 ; and rude and imperfect as it 

 was, the analogy of modern invention, especially 

 in watches, would lead us to think that it must 

 have been the fruit of several centuries of thought 

 and improvement. 



A portrait of this parent of modern time-keepers 

 may be interesting to our readers ; and, from its 

 comparative simplicity, will be well adapted as a 

 ground-work for further explanation of the mech- 

 anism of clocks and watches in their more complex 



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