PHYSICAL AND MATHEMATICAL SCIENCES. 97

for the cultivation of algebra. The origin of thisscience has been traced to India ; and it seems veryprobable that the Arabs derived their knowledge of itfrom nations further to the East. Their writers men-tion that Mahomet Ben Musa of Chorasan, (about A.n.959) distinguished among his countrymen for his mathe-matical knowledge, travelled into India for the purposeof acquiring further instruction in the science of algebra.The information we have of late years received respect-ing the algebra of the Hindoos, tends to give it a dis-tinct character of originality.

Though we are here speaking of science as flourishingin the East, we may yet include in the description theMoorish empire in Spain ; under which we find, amongthe most distinguished ornaments of Arabian science,Alhazen , who flourished in the eleventh century. Hisprincipal production is a treatise on optics. Before therediscovery of Ptolemy ’s work on the same subject, itwas supposed that Alhazen ’s was in a great degree copiedfrom it. The originality of Alhazen , and, in manyrespects, his superiority to Ptolemy , are now fully ad-mitted; his applications of geometry are of a very refinedand skilful description. He suggested the explanationof the apparent magnification of the heavenly bodiesnear the horizon, before referred to. He treated ofrefraction ; and gave an explanation of the cause oftwilight. His investigation of the atmospheric refrac-tion as applied to astronomy is the only point, perhaps,in which he is inferior to Ptolemy . He appears to havethrown out some good conjectures on the optical struc-ture of the eye, and remarks, that when correspondingparts of the retina of each eye are affected, we seehut one image. His writings are prolix, and withoutmethod.

The Tartar conquerors who succeeded the Arabs inthe East, were also zealous promoters of science, espe-cially of astronomy. The grandson of Gengis-khanfounded an observatory in Persia , and furnished it withthe best books and apparatus. Under his protection theH .