CHAP. V.

Of the Persian Astronomy in particular.

THE ancient persians, from the time of Darius Ochus, had made a great number of observations. They particularly applied themselves to determine the length of the solar year, to which they referred all the measures of time. Having fixed it's duration to 365 days fix hours, they sunk these six hours, or fractional part of a day, by intercalating a month of thirty days once in a hundred and twenty years; which amounts to the same as a day every four years in the julian account. They likewise placed this intercalary month succeflively the first in the year, the second, and so on; by which means it made a complete revolution through the year, and gave occasion to various religious ceremonies. When the persians were subjected to the yoke of the arabs, the practice of computing by lunar revolutions, which was followed by the conquerors, became that of the conquered likewise. But on But on the recovery of their freedom, they resumed their ancient method about the year 1079. At that time the persian astronomer Omar Cheyam, in order to rectify the ancient calendar of his nation, founded on the hypothesis of a year about eleven minutes too long, conceived the idea of adding a day every fourth year, seven times following, and then a day on the fifth year; which is the same thing as if

he

he had added eight days every thirty-third year. This system, which comes very near to the truth, was adopted, and has been retained by the persians.

Several of the persian emperors also zealously patronised astronomy. It was a kind of religion of the state. Chioniades, a greek author, who lived in the thirteenth century, relates that the persians were so jealous of their acquirements in this science, that the communication of them to foreigners was prohibited by a law, except on very rare occasions, which were left to the decision of the emperor. This prohibition was founded on a prophecy, which foretold, that the christians would one day overturn the persian empire by means derived from the science of astronomy. Chioniades himself found great difficulty in being admitted to receive lessons from the persian astronomers, though he had been strongly recommended by the emperor of Constantinople, then connected with the persian emperor by the ties both of friendship and interest. From this intercourse he brought back into Greece some astronomical tables, which, according to Bouillaud, were very accurate for the time when they were calculated.

A descendent of Genghis khan, called by some Holagu Ilecou khan, by others Houlagou khan, who conquered Persia about the year 1264, honoured the sciences, which he himself cultivated; and during the remainder of his life seemed to bend his mind solely to render them flourishing throughout the vast extent of his dominions. In the city of Maragha, near Tauris, the capital of Media, he built an observatory, at which he assembled a great number of astronomers;

and

and appointed Nassir Eddin, who has been mentioned above, their president. This society was a kind of academy, which was the more flourishing, as it received every sort of encouragement from a generous prince, who was himself very learned. Nassir Eddin composed several astronomical works, among which were a Theory of the Motions of the heavenly Bodies, a Treatise on the Astrolabe, and some astronomical tables, which he entitled Itecalic Tables, as a record of his gratitude to his benefactor. It is said that Houlagou, feeling himself near his end, caused himself to be removed to the residence of these learned men, in whose arms he wished to resign his last breath, considering them as the children of his glory, and it's best heralds.

His example was surpassed by a tatar prince, the famous Ulugh Beg, grandson of Tamerlane. Ulugh Beg not only encouraged the sciences as a sovereign, but is himself reckoned among the most learned men of his age. In the city of Samarcand, his capital, he established a numerous assembly or academy of astronomers; and caused larger and more perfect instruments, than had ever been seen, to be constructed for their use. He acquainted himself with all their labours, and observed the heavens with affiduity. Some historians relate, that, to determine the latitude of Samarcand, he employed a quadrant, the radius of which was equal to the height of the church of St. Sophia at Constantinople, or 180 feet: but the construction of so large a quadrant is physically impossible; and we have every reason to presume, that these historians, little acquainted with astronomy,

mistook a simple gnomon for a quadrant. The latitude of Samarcand was found to be 29 degrees 37 minutes. By means of the fame instrument, the obliquity of the ecliptic was fixed at 23 degrees, 30 minutes, 20 seconds: which, surpassing that of modern observations about two minutes, has led to the belief, that the obliquity of the ecliptic suffers a constant diminution; but this is a point, on which we have not sufficient information. Ulugh Beg composed several works, some of which are printed, and others are preserved in manuscript in a few libraries. The chief of them are a Catalogue of the Stars, and Astronomical Tables, the most perfect then known in the East. This prince deserved by his virtues and talents the homage of all the Earth; yet he was assassinated at the age of fifty-eight by his own son.

The troubles that followed this atrocious deed plunged the kingdom of Persia into a state of barbarism. The men of learning soon disappeared; and astronomy continued declining in this country to such a degree, that it is now a mere heap of astrological visions; and the persians scarcely know how to make a rude calculation of an eclipse by means of practical rules, which they follow by rote, without having the least knowledge of the theories, on which they were founded.

СНАР.

CHAP. VI.

State of Science among the Turks.

SOME rays from the sciences of the arabs penetrated to the turks. On the foundation of their empire, about the year 1220, medresses, or colleges, were instituted, in which geometry and astronomy were taught, as they still are. The first impulse given to the turks carried them to some length in the mathematics; but it gradually grew feebler, as it did with their masters. However, even in the present day the turks are not altogether so ignorant, as they are commonly supposed to be. Mr. Toderini, an italian author, who has written a work on the Literature of the Turks, asserts, that they are well skilled in arithmetic; that they make numerical calculations with extraordinary quickness; that some of them have carried algebra as far as we have done; that geometry is taught with success in their colleges; and lastly, that they cultivate astronomy for two cogent reasons, one of which is the necessity of regulating their time, and the other, their fondness for judiciary astrology, which cannot dispense with the assistance of astronomy itself. On this subject I shall say no more, and I shall not return again to a people, who, after all, nevermade any one discovery in the sciences.

CHAP.