THE CONTINUITY OF SCIENCE 49 



his son, the Caliphate of Bagdad was the center 

 of Arab science. ^Mathematics and astronomy were 

 especially cultivated ; an observatory was established ; 

 and the work of translation was systematically car- 

 ried on by a sort of institute of translators, who ren- 

 dered the writings of Aristotle, Hippocrates, Galen, 

 Euclid, Ptolemy, and other Greek scientists, into Ara- 

 bic. The names of the great Arab astronomers and 

 mathematicians are not popularly known to us ; their 

 influence is greater than their fame. One of them 

 describes the method pursued by him in the ninth 

 century in taking measure of the circumference of 

 the earth. A second developed a trigonometry of 

 sines to replace the Ptolemaic trigonometry of chords. 

 A third made use of the so-called Arabic (really 

 Hindu) system of numerals, and wrote the first work 

 on Algebra under that name. In this the writer did 

 not aim at the mental discipline of students, but 

 sought to confine himself to what is easiest and most 

 useful in calculation, " such as men constantly re- 

 quire in cases of inheritance, legacies, partition, law- 

 suits, and trade, and in all their dealings with one 

 another, or where the measuring of lands, the dig- 

 ging of canals, geometrical computation, and other 

 objects of various sorts and kinds are concerned." 



In the following centuries Arab institutions of 

 higher learning were widely distributed and the flood- 

 tide of Arab science was borne farther west. At 

 Cairo about the close of the tenth century the first 

 accurate records of eclipses were made, and tables 

 were constructed of the motions of the sun, moon, 

 and planets. Here as elsewhere the Arabs displayed 

 ingenuity in the making of scientific apparatus, celes- 



