Some information about the life of the great naturalist of the East Abu Sahl Masihiy is contained in the works of Beruni, Bayhaqi, ibn al-Kiftiy, ibn Abu Usaybia. In his treatise Geodesy, Beruni mentions the full name of the scientist as Abu Sahl Isa ibn Yahya al-Masihi. Abu Sahl al-Masihiy was born in 970 in the city of Jurjan (Gurgan) on the southeastern shores of the Caspian Sea. Masihiy has long served in the palace of the Emir of Jurjan, Qaboos ibn Vushmagir. In 995-997 he moved to Khorezm, Gurganj, first in the service of Mamun ibn Muhammad and then Ali ibn Ma'mun. For 16 consecutive years from 1004 onwards, he worked at the Mamun Academy alongside Beruni, Ibn Sina, Abul Hayr Hammar and other scholars, and served as the Academy’s scientific secretary. He is known in the East as a physician-scientist, writing works on Masihiy astronomy, mathematics, natural sciences, philosophy, logic, and especially medicine. Abu Sahl was a close friend of the Masihiy Beruni and Ibn Sina and mentored them in medicine. Ibn Sina studied the many theoretical and practical aspects of medicine from the Masihiy and benefited from the advice of his master in the preparation of the "Laws of Medicine". However, Masihiy did not live long in Khorezm. Before his conquest, Mahmud was on his way to Khorasan with his disciple Ibn Sina, when he fell seriously ill on the road in 1010 and died at the age of 40.