Meghnad Saha

Saha was born in 1893 in Seoratali, in the Dacca district of Bengal, then part of British India and now in Bangladesh. He continued his education despite economic hardship and faced caste discrimination as a student. He studied at Presidency College in Calcutta, where Satyendra Nath Bose was a classmate, and became a physicist and teacher at the University of Calcutta.

Saha's major contribution was to explain how the ionization of atoms in hot gases varies with physical conditions. His ionization equation describes the balance between successive ionization states in a gas in thermal equilibrium; it depends especially on temperature and the gas's electron density. Applied to stellar atmospheres, the theory made it possible to interpret observed spectral lines in terms of the physical conditions of stars. His work helped establish a quantitative basis for the analysis of stellar spectra and became an important contribution to astrophysics.

Saha's research extended beyond stellar spectra and thermal ionization to topics including spectroscopy, selective radiation pressure, molecular dissociation, the solar corona, radio propagation in the ionosphere and radio emission from the Sun. He helped develop research and teaching in physics in India, organizing active research groups at Allahabad and Calcutta. He played a major role in establishing the Institute of Nuclear Physics in Calcutta, now the Saha Institute of Nuclear Physics, and in building laboratories at the Indian Association for the Cultivation of Science. He founded and edited the journal Science and Culture, and helped establish scientific academies.

Saha was active in public affairs as well as science. He participated in national planning discussions and served as an elected independent member of India's Parliament. He was particularly interested in the role of science and industry in national development. His public writings addressed matters such as river management, railway reconstruction and power development.

The Saha ionization equation remains a standard tool in astrophysics for relating the ionization states of atoms to the physical conditions in a gas. Beyond this scientific legacy, Saha is remembered for building research institutions and communities in India and for engaging with the country's scientific and developmental priorities. The Royal Society's biographical memoir describes his work as spanning astrophysics, physics, institution building and public life.