Chats on Old Clocks. Arthur Hayden

and to determine seven as forming a week. Similarly one is curiously puzzled as to why he divided day and night into twenty-four parts, calling them hours.

      These speculations lead us farther afield than the scope of this volume. An examination of Babylonian and Greek measurements of time is too abstruse to be included in a volume of this nature. Nor is it necessary, however interesting such may be, to record the astronomical observations at Bagdad of Ahmed ibn Abdullah.

      We must commence with the known data that the earth revolves on its axis in twenty-four hours, or, to be more exact, in 23 hours 56 minutes 4 seconds. Astronomical clocks recording with scientific exactitude this phenomenon are on a plane apart, as are chronometers used by mariners. The astronomer uses a clock with numbers on its dial plate up to twenty-four; the common clock has only twelve hour numerals.

      To come straight to modernity, it must be recognized that the measurement of time scientifically and the measurement of time according to civil law are two different things.

      The mean Solar day used in the ordinary reckoning of time, by most modern nations, begins at midnight. Its hours are numbered in two series from 1 to 12—the first series, called A.M. (ante meridian), before midday, and the second series, P.M. (post meridian), after midday. This is a clumsy arrangement and leads to confusion. The leading railways of the world are beginning to use the series of twenty-four.

      Let it be granted that the day consists of twenty-four hours, which is the apparent Solar day; the starting-point was not always the same. The Babylonians began their day at sunrise, the Athenians and Jews at sunset, the ancient Egyptians and Romans at midnight.

      In passing, it should be noted that the day is measured astronomically by recording the period of the revolution of the earth on its axis, determined by the interval of time between two successive transits of the sun, the moon, or a fixed star over the same meridian.

      The Solar day is exactly 24 hours, the Lunar day is 24 hours 50 minutes, and the Sidereal day is 23 hours 56 minutes.

      Apparent Solar Time is shown by the sundial, and therefore depends upon the motion of the sun. Mean Solar Time is shown by a correct clock. The difference between Mean Time and Apparent Time, that is, between the time shown by the clock and the sundial, is called the Equation of Time, and in the Nautical Almanack, a Government publication, there are tables showing these differences.

      Day and Night.—Obviously the hours of darkness offered a greater problem to the horologist than the hours of light. His sundial was of no use at night and of little use on cloudy days. The hour-glass was not a piece of mechanism a man would wish to employ to record the night watches. Some other self-acting mechanism had to be devised.

      The interval between sunset and sunset, or sunrise and sunrise, or noon and noon, was divided by the Babylonians, who had a love for the duodenary system, into twenty-four hours. It is curious to read that "until the eighteenth century in England the hour was commonly reckoned as the twelfth part of the time between sunrise and sunset, or between sunset and sunrise, and hence was of varying durations" (Webster's New International Dictionary, 1914).

      The hour was further divided, also by the Babylonians, into periods of sixty minutes. It was the Babylonians who first divided the circle into 360 degrees, and Ptolemy followed this division.

      The dial of a clock was at first termed the hour-plate, as only hours were engraved upon it and only one hand was employed. Later, another hand was added, the minute hand, which travelled a complete circuit while the hour hand was travelling between two hour numerals. Later, again, a new sub-dial was added, and a seconds hand recorded the sixty seconds which made the minute. The term "second" was at first called "second-minute," denoting that it was the second division of an hour by sixty. The learned John Wilkins, Bishop of Chester, that extraordinary old savant, writes in 1650: "Four flames of an equal magnitude will be kept alive the space of sixteen second-minutes, though one of these flames alone, in the same vessel, will not last at most above twenty-five or thirty seconds."

      These dry facts may serve to whet the curiosity of the student in regard to the measurement of time and its origin. They add a piquancy to the clock dial as we now know it. Scientific it is, as one of man's most exact recorders of natural phenomena. That an exact timekeeper should be found in the pocket of every schoolboy would seem an astounding miracle to our ancestors two hundred years ago, or even less than a hundred years ago: