The Babylonians used a single peg with three concentric circles
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With a few sticks or pegs, the Egyptians could make their first simple observations. They selected a level area and drove one peg into the ground to mark the point of observation. The observer sitting at that point ordered his assistant to drive in another peg at the direction of the rising or setting Sun. This operation was repeated day after day until the observer found that the newly driven peg was directly in line with yesterday's. A few days later the direction began to reverse. The observer drove permanent pegs into the ground at the points farthest north and south. These pegs gave him the direction of the Sun at the solstices. Pegs driven halfway between these solstice points gave the line of the equinoxes, the beginning of spring and autumn.
The Babylonians used a single peg with three concentric circles. At noon in midwinter the shadow of the gnomon touched the outermost circle, the middle circle at the equinoxes and the inner circle at noon on midsummer's day, when the shadow was shortest. This was the instrument which Anaximander introduced into Greece in 590 B. C. It implied a knowledge of the meridian, but it gave direction only at the solstices, or at the equinoxes when for one day the Sun rises due east and west, from whatever part of the world it is viewed.
There is still another method of determining the equinoxes and solstices, which calls for no equipment whatever. The Egyptians observed the stars which rose shortly before the Sun at sunrise, and set shortly after the Sun at sunset. The Sun during its annual passage around the ecliptic makes a complete circuit in the heavens with its position changing every day. The ancient peoples regarded the stars as fixed points in the heavens so the approach of the Sun to various stars gives a measure of its passage along the ecliptic. Today if we see the constellation Aries near the western horizon at seven o'clock in the evening, we will have a rough sort of idea that the spring equinox is at hand. In a similar way the Egyptians observed the stars, and for their own purposes reckoned the passage of the year.
There was always purpose in Egyptian science. They had no love for the abstract sort of speculation in which the Greeks reveled. The story goes that if a Greek heard a geometrical proposition in the morning, he had constructed a theory of the universe by night.
That was not the Egyptian way. Each bit of Egyptian knowledge was adapted to some purpose. Herodotus said that the Egyptians were forced to learn geometry so that they could figure out how much private land was lost after a Nile flood, and he was more nearly correct than Aristotle who considered geometry a pursuit of the leisure class. But Aristotle was right in this--that only the powerful men in Egypt knew anything of scientific principles at all. Knowledge brought power, and accuracy had its advantages even among the primitive societies, as the potentates of Egypt were well aware. The priests had worked out the laws for determining seasons, but they kept their secrets to themselves, and surrounded the most simple natural laws with a kind of esoteric hocus-pocus that served to keep secret the bases of their established power.
Together with the kings, the priests caused their temples to be built for purposes of observation as well as worship. The earliest temples faced northeast or northwest, so that the rays of the rising or setting Sun on the day of the summer solstice would traverse the full length of the building, pass through a niche at the far end, and strike a little image, which was thus lighted on only one day of the year--the most important day in the Nile valley because it marked the time when the river began to overflow.
These temples gave far greater accuracy than any two sticks driven into the ground. No mischievous boy could alter the direction of a temple, and the structure lent dignity to the proceeding. As soon as the priests were thus divinely ordained with foreknowledge of the Nile flood, they could instruct the common people to take advantage of the precious water, and the agriculture of Egypt flourished.
About 3000 B. C. there came into Egypt from some other part of the world, a migration of peoples, who thought the equinoxes more important than the solstices. In all probability these people came from Mesopotamia, from the country which lies between the Tigris and the Euphrates rivers, where civilization had already reached a pitch as high as the Egyptian, and where plentiful traces of prehistoric irrigation have been found. But, unlike the Nile, both the Tigris and Euphrates overflow at the spring equinox. With true missionary spirit these peoples brought their religion, divested of its practicality, and built temples to the equinoctial Sun up and down the valley of the Nile.
It is impossible for us to tell just who these people were. The Mesopotamian influence, even then, spread over a vast territory. Usually the memory of such great migrations can be found imprinted in the folklore of the peoples who made them, exaggerated or depreciated, changed to suit dramatic tendency or the character of a hero, but still in essence the story of a migration. Of this one there is almost no remnant. But we do know that just before this time there was unrest on the continent of Asia. The Nomads of the pasture lands had begun to look with longing eyes on the fertile crops of the settled regions. Already the Semites had started their prolonged drift into Palestine. We know that some fifteen hundred years later, a nomad people beset by similar conditions wandered into the land of Egypt and stayed there until they were forcibly ejected by a Pharaoh whose violent anti-Semitic nationalism rose close to modern heights.
Whatever people may have contributed to this early migration, certainly "they waxed exceeding mighty, and the land was filled with them." Between 3000 and 2000 B. C. they seem to have triumphed over the original inhabitants. With them they brought a theory that the universe, or perhaps the Earth, was shaped like a pyramid with four corners, an idea which has persisted. Even today any man, when asked what has become of his school friends, is likely to reply, "Oh, they are scattered to the four corners of the Earth," although he knows perfectly well that the Earth does not have one corner, much less four. Tradition, even when erroneous, dies hard.
Influenced by these invaders, the Egyptians built their pyramids in the image of the universe, and faced them east and west. The Pyramid of Cheops at Gizeh is 481 feet high and 755 feet square, a miraculous achievement in structure and building. If the Egyptians desired to know the day of the equinox they had only to sight along the north or south sides to determine the position of the rising Sun. They could also tell the solstices by drawing a line north from the center of the pyramid, and marking the position of the Sun at noon by the shadow the pyramid cast. The shortest shadow was at the summer solstice--the longest was at the winter. The entrance way was designed as an observatory for their pole star. All this science was contained in a pyramid--and considering the magnificence of these early tombs it is a little startling to discover that the name we give to them was the ordinary Greek word for a cake. It is true that there was a similar Egyptian word that meant "ridge," but that could hardly apply and, as John Burnet points out, "The Greeks called 'crocodiles' 'lizards,' 'ostriches' 'sparrows,' and 'obelisks' 'meat-skewers,' so they may very well have called 'pyramids' 'cakes.'"
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