, Allacen, or Abdilazum, was a learned Arabian, a native of Bassorah. He wrote upon Astrology; and his work upon optics was printed in Latin, at Basil, in 1572, under the title of “Opticae Thesaurus,” by Risner. Alhazen was the first who shewed the importance of refractions in astronomy, so little known to the ancients. He is also the first author who has treated on the twilight, upon which he wrote a work, and takes occasion to speak also of the height of the clouds. He first, however, distinguished himself as a projector. He boasted frequently that he could construct a machine to prevent the inundations of the Nile. This being reported to the caliph, he offered him presents, workmen, and every species of encouragement; but Alhazen, having soon discovered | the impossibility of accomplishing his scheme, and dreadinothe anger of the caliph, put on a feigned madness, which he continued as long as the caliph lived. The rest of his life he spent, in writing, or in copying books, which he sold. He died at Cairo in 1038. Casiri, in his Bibl. Arab. Hisp. gives a long catalogue of his works, some of which are in the Bodleian, and some in the library of Leyden. The work above mentioned, edited by Risner, is supposed to have been of service to Kepler. 1


Universelle.-—Hutton’s Mathematical Dictionary. —Moreri.