Part 73

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.

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.

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?

Photo by James Arthur.

WATER CLOCKS FOR TELLING TIME

This picture shows the hour-glass or sand-glass. It is really a type of water-clock, being based on the same principle. The upper glass bulb was filled with sand and this sand fell through a little hole between the two bulbs. When the sand had all gone through, the glass was turned upside down and the operation repeated.

TIME-BOY OF INDIA.--WATER-CLOCK.

The Water-clock consisted of a large vessel filled with water, on the surface of which was placed a smaller vessel, really a gong, with a hole in the bottom. The water gradually filled the smaller vessel, and it sank. The Time-boy sat beside the Water-clock and as soon as the vessel sank he fished it out, emptied it, struck the gong one or more times and set it on the water again.]

During the night and also in cloudy weather the sun-dial was useless, and we read that the priests of the temples and monks of more modern times “went out to observe the stars” to make a guess at the time of night. The most prominent type after the shadow devices was the “water-clock” or “clepsydra,” but many other methods were used, such as candles, oil lamps, and in comparatively late times, the sand-glass. The fundamental principle of all water-clocks is the escape of water from a vessel through a small hole. It is evident that such a vessel would empty itself each time it is filled in very nearly the same time. The reverse of this has been used, as shown in the picture of the Time-boy of India. He sat in front of a large vessel of water and floated a bronze cup having a small hole in its bottom in this large vessel, and as the water ran in through the hole the cup sank. The boy then fished it up and struck one or more blows on it as a gong. This he continued and a rude division of time was obtained--while the boy kept awake!

The “Hon-woo-et-low,” Canton, China. Copper jars dropping water.]

The most interesting of all water-clocks was undoubtedly the “copper jars dropping water,” in Canton, China, where it can still be seen. Referring to the picture herewith and reading the four Chinese characters downwards the translation is “Canton City.” To the left and still downwards, “Hon-woo-et-low,” which is, “Copper jars dropping water.” Educated Chinamen inform me that it is over 3000 years old. The little open building or tower in which it stands is higher than surrounding buildings. It is, therefore, reasonably safe to state that the Chinese had a weather and time station over 1000 years before our era.

Photo by James Arthur.

TOWER OF THE WINDS.

This tower is located at Athens, Greece. It was built about 50 B.C. It is octagonal in shape and had at one time sun-dials on each of its eight sides. On top was a bronze weather vane from which it derived its name.]