Page:The chronology of ancient nations (IA chronologyofanci00biru).djvu/34

means of the parts of the smallest circle. I refer to the smallness of the instruments of observations in comparison with the vastness of the bodies which are to be observed. On this subject I have enlarged in my book, called Kitâb-alistishhâd bikhtilâf-al'arṣâd.

During this time, i.e. during one revolution of the sun in the ecliptic, the moon completes a little less than ⁠12+1/2⁠ revolutions, and has 12 lunations. This space of time, i.e. the 12 revolutions of the moon in the ecliptic, is, technically, the lunar year, in which the fraction (beyond the 12 revolutions), which is nearly 11 days, is disregarded. The same fact, further, is the reason why the ecliptic was divided into 12 equal parts, as I have explained in my book on the investigation of rays and lights; the same which I had the honour to present to His Highness. May God increase his majesty!

In consequence, people distinguish two kinds of years—the Solar year and the Lunar year. They have not used other stars for the purpose of deriving years from them, because their motions are comparatively hidden, and can hardly ever be found out by eyesight; but only by astronomical observations and experiments. Further (they used only sun and moon for this purpose), because the changes of the particles of the elements and their mutual metamorphoses, as far as time and the state of the air, plants and animals, etc., are concerned, depend entirely upon the motions of these two celestial bodies, because they are the greatest of all, and because they excel the other stars by their light and appearance; and because they resemble each other. Afterwards people derived from these two kinds of years other years.

The Solar Year.—According to the statement of Theon, in his Canon, the people of Constantinople, and of Alexandria, and the other Greeks, the Syrians and Chaldseans, the Egyptians of our time, and those who have adopted the year of Ahmu'ta-ḍid-billâh, all use the solar year, which consists of nearly ⁠365+1/4⁠ days. They reckon their year as 365 days, and add the quarters of a day in every fourth year as one complete day, when it has summed up thereto. This year they call an intercalary year, because the quarters are intercalated therein. The ancient Egyptians followed the same practice, but with this difference, that they neglected the quarters of a day till they had summed up to the number of days of one complete year, which took place in 1,460 years; then they intercalated one year, and agreed with the people of Alexandria and Constantinople as to the beginning of the year. So Theon Alexandrinus relates.

The Persians followed the same rule as long as their empire lasted; but they treated it differently. For they reckoned their year as 365 days, and neglected the following fractions until the day-quarters had summed up in the course of 120 years to the number of days of one complete month, and until the fifth parts of an hour, which, according to their opinion, follow the fourth parts of a day (i.e. they give the