Elementary arithmetic, with brief notices of its history... by Robert Potts.

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ON THE DIVISIONS AND MEASURES OF TIME.

The names given to the seven days of the week by our AngloSaxon ancestors before their conversion to Christianity continue in
use at the present time. It is a singular fact that these names have
descended unaltered and unchanged by the revolution which took
place in England when it was subjugated by William Duke of
Normandy. The names of the seven days of the week are formed.
by annexing the word daeg, a day, to the names of the Saxon
deities: Sun, Mloon, Tuisco, Wodin, Thor, Friga, Seater. The word
se'nniglt (seven night) is used to denote a period of seven days,
and bears on its face a faint trace both of the day beginning at even,
and the original appointment of the seventh day; so also its kindred
fortnight (fourteen night), fourteen, or twice seven nights.
In addition to the divisions and measures of time already noticed,
other divisions of the day have been made both for the purposes of
science and the convenience of human life. It is recorded by Herodotus (ii. 109) " that the sundial,1 the gnomon, and the division of the
1 The sundial is a contrivance to mark the hours of the day while the sun
shines above the horizon. It is not known when the Hebrews adopted the division
of the day into hours: there is no trace of it in the Pentateuch. The mention of
the dial of Ahaz in the time of Hezekiah, B.o. about 730 (2 Kings xx. 9-11; Isa.
xxxviii. 8), implies some sort of division, but the records give no account of the
magnitude of the degrees, or what portion of time was marked by them. The word
translated "hour," in Dan. iii. 19, cannot mean an hour in the sense of a twelfth
part of a day, but would be more correctly rendered "moment," as the context
suggests.
Anaximander, a companion and disciple of Thales, is reported by later Greek
writers to have invented the sundial. lie died about B.C. 547, in the sixty-fourth
year of his age (Diogenes Laertius). If he derived his knowledge of the sundial
from the Babylonians, he may have been the first to introduce the knowledge of it
to the Greeks. The claim of the Greeks in later times to the invention of the sundial can scarcely be correct; it is, however, highly probable that the Greeks made
improvements of the dials they received, just as they advanced the knowledge of
geometry and other sciences which their predecessors originally brought from Egypt.
There is in the British Museum a stone block on which are marked lines which
clearly indicate that they are the lines of an ancient sundial. It is supposed to be
the oldest specimen of sundials known to be extant. The reader will find some
interesting information in "An Inquiry into the Geometrical Character of the Hour
Lines upon the Antique Sundials," by T. S. Davies, Esq., F.R.S., printed in the
Transactions of the Royal Society of Edinburgh, February, 1831.
The Clepsydra, or Water-clock, was a cylindrical vessel with a small hole at tlho
bottom. On the side of the vessel from the top downwards the hours were marked.
The vessel was filled with water, which, in the space of a day, flowed out through
the aperture; an index, while floating, pointed to the hours as the surface of the
water gradually subsided. They were of various kinds, but all of them were inaccurate measurers of time, as the water would flow through the orifice in the bottom of
the vessel more rapidly when full than when nearly empty, on account of the pressure
being greater according to the depth of the water.
Ctesibius of Alexandria, in the time of Euergetes II., invented a more percct
hydraulic clock, and more simple than those which were then known. It is described
by Aristotle (Prob. Sec. 16, p. 933) and mentioned by Aristophanes as well known
in his time. Vitruvius affirms that Pliny relates that it was introduced into Rome
by Scipio Nasica (Pliny vii. 37; ii. 76, in HIorologium).
The clock as an instrument for the measurement of time was unknown to the
Greeks and Romans. The invention of this complicated mnachine belongs to a mlore
improved state of scientific knowledge. The invention of the clock (probably the
balance clock) is ascribed to the Arabians, about the year 801 A.D.
Dante, who was born in 1205 and died 1321, mentions a clock in Italy that
struck the hours, which is the earliest instance on record. A clock about 1288 was
fixed in the famous clock-house in Westminster Hall. In 1292 a similar clock was
constructed for the cathedral of Canterbury; Peter Lightfoot constructed a clock at
Glastonbury in 1325 (Brady's " Claris Calend.," vol. i., p. 8). In Ryiner's Foedera