ISLAM’S CONTRIBUTION TO MODERN SCIENCE

to practical mathematics, can hardly be overestimated. Another mathematical improvement was the introduction into trigonometry of the sine—the half-chord of the double arc—instead of the chord of the arc itself which the Greek astronomers had employed. This improvement was due to the famous astronomer and mathematician Al-Battani (d. AD 929). Astronomy For measurement of the Earth, instead of trusting to the measurement of angles, the Arabs decided to measure directly degree of the Earth’s surface. Selecting a level plain in Mesopotamia for the experiment, one party of the surveyors progressed northward, another party southward, from a given point to the distance of one degree of arc, as determined by astronomical observations. The result found was fifty-six miles for the northern degree, and fifty-six and two-third miles for the southern. It is interesting to note that the two degrees were found of unequal lengths, suggesting that the Earth is not a perfect sphere—a suggestion the validity of which was not to be put to the test of conclusive measurements until about the close of the eighteenth century. The Arab measurement was made in the time of Caliph Abdullah al-Mamun, the son of the famous Harun-al-Rashid. Harun-al-Rashid (d. AD 809) sent Charlemagne, as a token of friendship, a marvellous clock which let fall a metal ball to mark the hours. This mechanism, which is alleged to have excited great wonder in the West, furnishes yet another instance of Arabian practicality. Al-Battani made the important discovery of the motion of the solar apogee. He found that the position of the sun among the stars, at the time of its greatest distance from the Earth, was not what it had been in the time of Ptolemy. The Greek astronomer placed the sun in longitude 65 degrees, but Al-Battani found it in longitude 82 degrees, a distance too great to be accounted for by inaccuracy of measurement. Physical Science Ibn al-Haytham’s work on Optics, published about the year AD 1100, found great favour throughout the medieval period. His original investigations of the eye, and the names given by him to various parts In medieval Europe, Arabian science came to be regarded with superstitious awe, and the works of certain Arabian physicians were exalted to a position above all the ancient writers.