TIME-RECKONING. 109 
singular consequence, the number of hours were made constant 
between sunrise and sunset, and instead of being equal in length, the 
hour varied with the length of daylight. Whatever the moments of 
sunrise and sunset, the interval of light was divided into 12 parts. 
If the sun rose at 4 a.m. and set at 8 p.m., according to our notation, 
each hour would be equal in length to 80 of our minutes. Old habits 
are so strong that this constantly varying system was adhered to long 
after mechanical time-keepers were introduced, and attempts were 
made to regulate clocks to tell the unequal hours. Like the Romans, 
the Greeks divided the intervals of light between sunrise and sunset, 
whatever its length, into 12 equal parts, subject to change from day 
to day. The custom of making the hours variable is still followed 
by some eastern nations. 
The system of dividing the day by the rising and setting of the 
sun makes the hours indefinite periods, as they continuously change 
with the seasons. Except at the equinoxes, the hours of the night 
and day can never be of equal length. Near the equator the varia- 
tions are least ; they increase with every degree of latitude until the 
arctic and antarctic circles are reached, within which a maximum is 
attained. Even in the latitude of Rome, the length of the hours of 
daylight and darkness under this system have an extreme difference 
of 75 minutes. In Spitzbergen the sun sets about the beginning of 
November, and remains below the horizon for more than three 
months. It does not set for an equal period after the middle of May. 
Sun dials had two great defects, they were unserviceable at night 
and during cloudy weather. The clepsydra or water clock was 
accordingly introduced at Rome about 158 B.C., by Scipio Nasica 
Corculum. It measured time by allowing water to escape through 
an orifice in a vessel, as sand flows through a modern sand glass. 
Subsequently some sort of toothed-wheel work was applied to the 
clepsydra by Ctesibius (A. D. 120). Diurnal and nocturnal time 
was measured in this or some other rude manner for many centuries, 
Besides sun dials, gnomons and clepsydre, all of which appear to 
have been known to the Egyptians, Indians, Chaldeans, Babylonians 
and Persians long before their Introduction at Rome, mention is 
made of a contrivance by which a mechanical figure dropped a stone 
into a brazen basin every hour, producing a loud sound which for a 
great distance announced the divisions of time. King Alfred em- 
ployed as a time-keeper six wax candles, each 12 inches long. Three 
