Instead of writing on papyrus or parchment, or cutting or painting their inscriptions on the walls of temples, tombs, and palaces, as did many other ancient nations, the Babylonians impressed theirs on clay tablets, which were preserved with or without burning. In the later period of Babylonian independence and prosperity, the writing was syllabic. There were about one hundred groups of cuneiform or wedge-shaped marks for as many syllables containing one consonant; and about two hundred marks for syllables each containing two consonants. Alphabetic characters did not come into use until Babylonia became part of the Persian Empire. With the syllabic character, the older word signs were often mingled, and the preservation of these implied that there was a time when word signs were used exclusively in Babylonia for writing.
It was mainly because of their superiority in arithmetic, mathematics, and astronomy that in the VIIth and VIth centuries BC the Babylonians were reputed to be the most learned of nations. In their arithmetic, much prominence was given to the number sixty; and they had simple and complex multiplication tables. Of the latter, one gave the squares and another the cubes of all the numbers from one to sixty. They divided the day into twelve hours, the hour into sixty minutes, and the minute into sixty seconds. They divided the ecliptic into three hundred and sixty degrees, presumably adopting that number because it was the product of twelve multiplied by thirty, those multipliers being "the nearert numbers to the lunations in a year, and to the days in a lunation."* They divided the lunar month into four weeks of seven days each, assigned a day to each of the seven planets, and called the last day of the week the sabbath, or rest of the soul.
They made maps and catalogues of the stars, divided them into groups, distinguished planets and comets from fixed stars, understood the relative distances of many planets from the earth, recorded occultations of planets by the sun and moon, observed the revolution of the stellar system, traced the track of the sun round the firmament, and divided its course into twelve sections, giving to each its constellation, name, and distinctive sign. It is from them that modern civilization has derived its zodiac and its divisions of the circle, of the day, and of the year. These measures must have been devised by scholars who had profited by the experience and the lessons of many centuries; and after adoption by the scholars, they were legalized by the government, superseding older and ruder standards. Of the many wonderful achievements of the Babylonians, one of the most difficult was the tracing of the sun through the sky, along a path which in the day is hidden, by the glare of light, and at night is discoverable to the reason and not to direct vision. Different languages were spoken in the Euphrates Valley, and these were studied with the aid of dictionaries and grammar.
Their astronomical observations were continued for at least nine centuries, and their records for so long a time were used by Ptolemy the astronomer, in the middle of the IInd century AD. Aristotle said that their astronomical observations ran back 31,000 years. They invented the astrolabe to measure the altitude of stars above the horizon. They recorded lunar eclipses, and by their tables found that these phenomena recur in cycles of two hundred and twenty-three lunations or periods of about nineteen years. They measured with approximate accuracy the solar day, the lunar revolution, and the solar year. The last, according to their calculations, was about three hundred and sixty-five days and a quarter. They invented two kinds of sun-dials for the measurement of time, - the vertical pillar and the more precise rectangular triangle with its hypothenuse pointing to the pole-star. They also invented the water-clock, to measure time, and with this they calculated the speed of the sun's movement and the diameter of its disk in relation to the length of its orbit. "At the moment when the sun was seen in the sky on the morning of the equinox, a jar filled with water was opened. From this the water was allowed to run into a second small jar, till the orb of the sun was completely visible; then it ran into a third and larger jar till the sun was again seen on the horizon on the following morning. They concluded that the diameter of the sun must stand in the same proportion to the cycle it passed through as the water in the small jar stood to the water in the large one. Hence they found that the diameter of the sun was contained seven hundred and twenty times in its course.
There can be no doubt that the Babylonian astronomy was more truly scientific than the Egyptian, and that it reached the highest perfection attainable without the aid of optical instruments. The Chaldeans knew the synodic period of the moon, the equinoctial and solstitial points, the true length of the year as dependent on the annual course of the sun (within a narrow limit of error), and even the precession of the equinoxes. But as might have been expected from their want of accurate instruments, they made a mistake in the amount of the precession and calculated it at thirty seconds instead of fifty. Hence their great cosmical year-that is, one complete revolution of the equinoctial points among the fixed stars -was made too long in like proportion, namely, 43,200 solar years instead of 26,000, to use round numbers.
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