He was a mathematician and scientist with a special interest in astronomy and compiled a famous biographic encyclopedia of science that quickly became popular in the empire and the Islamic East.
[6] The Ṭabaqāt al-ʼUmam (Tabaqāt) composed in 1068 is an early "history of science"[9] that comprises biographies of the scientists and scientific achievements of eight nations.
In the field of nations are the Indians, Persians, Chaldeans, Egyptians, Greeks, Byzantines, Arabs and Jews (in contrast to others not disposed, such as Norsemen, Chinese, Africans, Russians, Alains and Turks).
Ṣāʿid offers an account of the individual contribution each nation makes to the various sciences of arithmetic, astronomy, and medicine, etc., and of the earliest scientists and philosophers, from the Greeks, – Pythagoras, Socrates, Plato and Aristotle[n 3] – to the Roman and Christian scholars of the 9th and 10th centuries in Baghdad.
The second half of the book contains Arab-Islamic contributions to the fields of logic, philosophy, geometry, the development of Ptolemaic astronomy, observational methods, calculations in trigonometry and mathematics to determine the length of the year, the eccentricity of the Sun's orbit, and the construction of astronomical tables, etc.