What Is Time?
Time, as a separate entity, has not yet been defined in language.
Definitions will be found to be merely explanations of the sense in
which we use the word in matters of practical life. No human being can
tell how long a minute is; only that it is longer than a second and
shorter than an hour. In some sense we can think of a longer or shorter
period of time, but this is merely comparative. The difference between
50 and 75 steps a minute in marching is clear to us, but note that we
introduce motion and space before we can get a conception of time as a
succession of events, but time, in itself, remains elusive.
In time measures we strive for a uniform motion of something and this
implies equal spaces in equal times; so we here assume just what we
cannot explain, for space is as difficult to define as time. Time
cannot be “squared” or used as a multiplier or divisor. Only numbers
can be so used; so when we speak of “the square of the time” we mean
some number which we have arbitrarily assumed to represent it. This
becomes plain when we state that in calculations relating to pendulums,
for example, we may use seconds and inches--minutes and feet--or
seconds and meters--and the answer will come out right in the units
which we have assumed. Still more, numbers themselves have no meaning
till they are applied to something, and here we are applying them to
time, space and motion; so we are trying to explain three abstractions
by a fourth! But, happily, the results of these assumptions and
calculations are borne out in practical human life, and we are not
compelled to settle the deep question as to whether fundamental
knowledge is possible to the human mind.
What Was Man’s First Division of Time?
Evidently, man began by considering the day as a unit and did not
include the night in his time-keeping for a long period. “And the
evening and the morning were the first day,” Gen. i, 5; “Evening and
morning and at noonday,” Ps. lv, 17, divides the day (“sun up”) in two
parts. “Fourth part of a day,” Neh. ix, 3, shows another advance. Then
comes, “are there not twelve hours in a day,” John xi, 9. The “eleventh
hour,” Matt. xx, 1 to 12, shows clearly that sunset was 12 o’clock. A
most remarkable feature of this 12-hour day, in the New Testament, is
that the writers generally speak of the third, sixth and ninth hours,
Acts ii, 15; iii, 1; x, 9. This is extremely interesting, as it shows
that the writers still thought in quarter days (Neh. ix, 3) and had
not yet acquired the 12-hour conception given to them by the Romans.
They thought in quarter days even when using the 12-hour numerals!
Note, further, that references are to “hours”; so it is evident that
in New Testament times they did not need smaller subdivisions. “About
the third hour” shows the mental attitude. That they had no conception
of our minutes, seconds and fifth-seconds becomes quite plain when
we notice that they jumped down from the hour to nowhere, in such
expressions as “in an instant--in the twinkling of an eye.”
Before this the night had been divided into three watches (Judges vii,
19). Poetry to this day uses the “hours” and the “watches” as symbols.
This twelve hours of daylight gave very variable hours in latitudes
some distance from the equator, being long in summer and short in
winter. The amount of human ingenuity expended on time measures so as
to divide the time from sunrise to sunset into twelve equal parts is
almost beyond belief. In Constantinople, to-day, this is used, but in a
rather imperfect manner, for the clocks are modern and run twenty-four
hours uniformly; so the best they can do is to set them to mark twelve
at sunset. This necessitates setting to the varying length of the days,
so that the clocks appear to be sometimes more and sometimes less
than six hours ahead of ours. A clock on the tower at the Sultan’s
private mosque gives the impression of being out of order and about six
hours ahead, but it is running correctly to their system. Hotels in
Constantinople often show two clocks, one of them to our twelve o’clock
noon system. Evidently the Jewish method of ending a day at sunset is
the same and explains the command, “let not the sun go down upon thy
wrath,” which we might read, “do not carry your anger over to another
day.”
This simple line of steps in dividing the day and night is taken
principally from the Bible because every one can easily look up the
passages quoted and many more, while quotations from books not in
general use would not be so clear.
How Did Man Begin to Measure Time?
Now, as to the methods of measuring time, we must use circumstantial
evidence for the prehistoric period. The rising and the going down of
the sun--the lengthening shadows, etc., must come first, and we are on
safe ground here, for savages still use primitive methods like setting
up a stick and marking its shadow so that a party trailing behind can
estimate the distance the leaders are ahead by the changed position of
the shadow. Men notice their shortening and lengthening shadows to this
day. When the shadow of a man shortens more and more slowly till it
appears to be fixed, the observer knows it is noon, and when it shows
the least observable lengthening then it is just past noon. Now, it is
a remarkable fact that this crude method of determining noon is just
the same as “taking the sun” to determine noon at sea. Noon is the time
at which the sun reaches his highest point on any given day.
[Illustration: The Sun-dial is only an improvement on the stick which
cast a shadow which enabled man to tell the time of day at any hour.
The shadow moves around the dial, falling on the numbers on the circle.]
How Is the Time Calculated at Sea?
At sea this is determined generally by a sextant, which simply measures
the angle between the horizon and the sun. The instrument is applied a
little before noon and the observer sees the sun creeping upward slower
and slower till a little tremor or hesitation appears, indicating that
the sun has reached his height--noon. Oh! you wish to know if the
observer is likely to make a mistake? Yes, and when accurate local time
is important, several officers on a large ship will take the meridian
passage at the same time and average their readings, so as to reduce
the “personal error.” All of which is merely a greater degree of
accuracy than that of the man who observes his shadow.
The gradual development of the primitive shadow methods culminated in
the modern sun-dial. The “dial of Ahas” (Isa. xxxviii, 8), on which
the sun went back ten “degrees,” is often referred to, but in one of
the revised editions of the Bible the sun went back ten “steps.” This
becomes extremely interesting when we find that in India there still
remains an immense dial built with steps instead of hour lines.
In a restored flower garden, within one of the large houses in the
ruins of Pompeii, may be seen a sun-dial of the Armillary type,
presumably in its original position. It looks as if the plane of the
equator and the position of the earth’s axis must have been known to
the maker.
Both these dials were in use before the beginning of our era and were
covered by the great eruption of Vesuvius in 79 A.D., which destroyed
Pompeii and Herculaneum.
~THREE GREAT STEPS IN MEASURING TIME~
Modern sun-dials differ only in being more accurately made and a few
“curiosity” dials added. The necessity for time during the night, as
man’s life became a little more complicated, necessitated the invention
of time machines. The “clepsydra,” or water-clock, was probably the
first. A French writer has dug up some old records putting it back
to Hoang-ti 2679 B.C., but it appears to have been certainly in use
in China in 1100 B.C., so we will be satisfied with that date. In
presenting a subject to the young student it is sometimes advisable to
use round numbers to give a simple comprehension and then leave him to
find the overlapping of dates and methods as he advances. Keeping this
in mind, the following table may be used to give an elementary hint of
the three great steps in time measuring.
Shadow time, 2000 to 1000 B.C.
Dials and water-clocks, 1000 B.C. to 1000 A.D.
Clocks and watches, 1000 to 2000 A.D.
Gear-wheel clocks and watches have here been pushed forward to 2000
A.D., as they may last to that time, but no doubt we will supersede
them. At the present time science is just about ready to say that a
time measurer consisting of wheels and pinions--a driving power and a
regulator in the form of a pendulum or balance, is a clumsy contrivance
and that we ought to do better very soon.
It is remarkable how few are aware that the simplest form of sun-dial
is the best, and that, as a regulator of our present clocks, it is
good within one or two minutes. No one need be without a “noon-mark”
sun-dial; that is, every one may have the best of all dials. Take a
post or any straight object standing “plumb,” or best of all the corner
of a building. In the case of the post, or tree trunk, a stone (shown
in solid black) may be set in the ground; but for the building a line
may often be cut across a flagstone of the footpath. Many methods may
be employed to get this noon mark, which is simply a north and south
line: Viewing the pole star, using a compass (if the local variation
is known) or the old method of finding the time at which the shadow of
a pole is shortest. But the best practical way in this day is to use a
watch set to local time and make the mark at 12 o’clock.
[Illustration:
Drawing by James Arthur.
A form of Sun-dial that is as good to-day as any dial for determining
noon.]
On four days of the year the sun is right and your mark may be set at
12 on these days, but you may use an almanac and look in the column
marked “mean time at noon” or “sun on meridian.” For example, suppose
on the bright day when you are ready to place your noon mark you read
in this column 11.50, then when your watch shows 11.50 make your noon
mark to the shadow and it will be right for all time to come. Owing
to the fact that there are not an even number of days in a year, it
follows that on any given yearly date at noon the earth is not at the
same place in its elliptical orbit, and the correction of this by the
leap years causes the equation table to vary in periods of four years.
The centennial leap years cause another variation of 400 years, etc.,
but these variations are less than the error in reading a dial.
How Did Men Tell Time When the Sun Cast No Shadows?
[Illustration:
Photo by James Arthur.