Sunrise, noon and sunset: these three simple divisions of the day were used by the earliest peoples
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We can only guess how the Egyptians worked out the observations. They may have used equal altitudes of the Sun, marked their directions and bisected the angle. Possibly they employed the equal altitudes of stars, or bisected the extreme angles of the pole star. Since any definite knowledge of them begins with pyramid inscriptions and since they had worked out a method of determining the meridian before the pyramids were built, we have no knowledge of their ingenuity.
Sunrise, noon and sunset: these three simple divisions of the day were used by the earliest peoples, and continued in use far into classical times. Homer sang of no others: and the Romans never reckoned by hours until five centuries after the "Foundation of the City." But the peoples along the eastern Mediterranean belonged to an older civilization. They had found need to divide the day, even before they could reckon the meridian line. In Babylonia, at least, some such system as hours probably preceded any knowledge of "high" noon.
It is often said that the oldest sundial of all was a pyramid. That may be true; but we are not entitled to the deduction that the pyramids were built for astronomical purposes. Primarily they were intended to house the body of the king while his spirit was crossing the lake of waterlilies, tricking hostile gods, and generally encountering wild adventures in his afterlife. Among his peoples, his spirit alone was entitled to this immortality. The pyramid was certainly a symbol of the king rising to meet the Sun God; but its time-telling features may have been purely incidental. We should really be rather surprised if these gigantic stone structures, built to face the cardinal points, endowed with all the knowledge and resource of the age, did not tell time in some way or other.
The first purposely constructed sundial which has come down to us was made some twelve hundred years after the erection of the pyramids. Thutmose III, King of Egypt in 1500 B. C., made a sundial, and inscribed it with his own name.
We have reconstructed this sundial for the latitude of Denver. We took two narrow boards and set one horizontal, the other vertical. On the long horizontal board we drew lines to mark the months, and curves to show the hours. At all times the instrument must be turned, so that the short vertical board casts a shadow straight across the markings. Within the current month the path of the shadow falls across the hour of the day. If we are careful to keep the instrument straight, and consult it only in the midmorning and the midafternoon, we find that it tells time very well indeed.
The part that casts the shadow on any sundial is a pointer. The Greeks called it a "knower," or in their language a gnomon. We take this opportunity of introducing it to you with due formality, and great ceremony. You will meet it frequently throughout this chapter, and we hope, having made its acquaintance, you will remember it.
The dial of Thutmose depended entirely upon the altitude of the Sun, not like modern sundials, partly upon the longitudinal position of the Sun in the heavens. With this arrangement it cannot possibly show us the time of sunrise or sunset, for then the shadows are infinitely long, and our board is, alas, only finite. If the board were long enough, we could tell the first hour after sunrise; the second is always easy to mark, and so until the sixth hour which corresponds to what we call noon.
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