1890-91.] REFORMS IN TIME RECKONING. 129 



intervals in the eastern horizon, and the intervals were thus denoted 

 with proximate accuracy. By analogy the day from sun-rise to sun-set 

 was similarly subdivided ; hence the division of the diurnal period 

 embracing day-light and darkness, into two portions, each of which was 

 subdivided into twelve hours. The modern practice differs from ancient 

 usage only in the initial points of division. We reckon from mid-day 

 and midnight instead of from sun-rise and sun-set. The ancients had 

 an absolutely distinct reckoning for the night, and another for the day, 

 and they employed for the duty of observation during these periods two 

 distinct classes of watchers. 



Both in Greece and Rome "gnomons" were erected in open ground 

 for the public benefit, the length of the shadows of which denoted the 

 several hours. Magistrates were charged with the duty of watching the 

 shadow, and announcing in a loud voice the moment of mid-day, morning, 

 and evening. A few persons of wealth maintained their private gnomons 

 with slaves to watch the progress of the shadow, and at intervals to 

 announce its length. It is generally supposed that the great obelisks 

 of Egypt, examples of which still remain, were the clocks of the ancients. 

 One fact was early noticeable, that the gnomon or obelisk, whatever its 

 length, and whatever the season, cast its shortest shadow at an invariable 

 period of the day, and thus mid-day naturally became established at an 

 early date as an important point of time. 



An advance was made in the art of measuring the passage of the sun 

 by the introduction of sun-dials, by which a greater degree of precision 

 was obtained. Herodotus tells us that the concave dial and the ordinary 

 sun-dial were brought from Egypt, with the division of the period of 

 direct sunlight into twelve parts, all of which " the Greeks learned from 

 the Babylonians." 



Obviously the hours, being each a twelfth part of the two intervals 

 between sun-rise and sun-set, varied in length in the different months. 

 Throughout the temperate zone, hours determined on this principle 

 would constantly vary. In one half the year the hours of the night, in the 

 other half those of the day, would be the longest. Only twice in the year, 

 that is to say, at the equinoxes, would the hours be of uniform length. 

 In some parts of the temperate zone the hours in summer would be, 

 under this system, double the length of the hours in winter, and vice 

 versa. As the reckoning began with sun-rise and sun-set, these epochs 

 coincided with the twelfth hour of the previous half-day. Mid-day and 

 midnight each would be the sixth hour of the respective days and nights. 



Gradually mechanical contrivances were introduced to overcome the 

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