HINDU, ARABIAN AND MOORISH SCIENCE 163 



a cubic equation was solved by the aid of intersecting conic sec- 

 tions. There is no definite separation of algebra and arithmetic, 

 and the former, in spite of relatively rapid development, remains 

 entirely rhetorical. The division line of fractions is introduced 

 and the check of computation by "casting out nines." 



In Physics, Al-Hazen (965 ? 1038) wrote a work on optics 

 enunciating the law of reflection and making a study of spherical 

 and parabolic mirrors. He also devised an apparatus for studying 

 refraction, being probably the first physicist to note the magnify- 

 ing power of spherical segments of glass i.e. lenses. He gave 

 a detailed account of the human eye, and attempted to explain 

 the change of apparent shape of the sun and the moon when ap- 

 proaching the horizon. The Arabs employed the pendulum for 

 time measurement, and tabulated specific gravities of metals, etc. 

 In the words of a modern physicist : 



The Arabs have always reproduced what came down to them from 

 the Greeks in thoroughly intelligible form, and applied it to new prob- 

 lems, and thus built up the theorems, at first only obtained for par- 

 ticular cases, into a greater system, adding many of their own. They 

 have thus rendered an extraordinarily great service, such as would 

 correspond in modern times to the investigations which have grown 

 out of the pioneer work of such men as Newton, Faraday and Rbntgen. 



Wiedemann. 



ARABIAN ASTRONOMY. In connection with astronomy the 

 Arabs, following Greek precedents, developed trigonometry, in- 

 troducing sines and other functions since current. They used 

 masonry quadrants of large size, and even a combination of a 

 horizontal circle with two revolving quadrants mounted upon it, 

 foreshadowing the modern theodolite. Better and more com- 

 plete observational data facilitated, and at the same time de- 

 manded, improved mathematical methods, while the necessary 

 computations were accomplished much more economically, through 

 the use of the decimal number system. Haroun Al-Raschid sent 

 to Charlemagne an ingenious water clock, while under his suc- 

 cessor, Al-Mamun, two learned mathematicians were commis- 

 sioned to measure a degree of the earth's circumference. 



