Sisir Kumar Mitra

Sisir Kumar Mitra was a pioneering Indian physicist who made significant contributions to the fields of radio physics and atmospheric science. He is regarded as the founder of ionospheric science and radio technology in India. He was also a distinguished teacher, administrator, and popularizer of science. Mitra was born on 24 October 1890 in Konnagar, a suburb of Kolkata, in the Bengal Presidency of British India (now in West Bengal, India). He was the third son of Joykrishna Mitra, a schoolteacher and a follower of the Brahmo Samaj movement, and Saratkumari Mitra, a physician who was one of the first Indian women to qualify as a doctor from the Campbell Medical School in Kolkata. Mitra had a keen interest in science from an early age, inspired by the stories of Ramchandra Chatterjee, a Bengali aeronaut who had made a solo balloon flight in 1889. Mitra received his school education at the Bhagalpur District School, where his mother worked at the Lady Dufferin Hospital. He then moved to Kolkata to study at the Presidency College, where he had the opportunity to learn from eminent scientists like Jagadish Chandra Bose and Prafulla Chandra Ray. He completed his M.Sc. degree in physics in 1912 with a gold medal. He then joined the T.N.J. College at Bhagalpur as a lecturer, and later moved to the Christian College at Bankura. In 1916, Mitra was appointed as a lecturer in the newly formed postgraduate department of physics at the University of Calcutta. He started his research work under the guidance of C.V. Raman, who was then a professor of physics at the same university. Mitra worked on the interference and diffraction of light, and obtained his D.Sc. degree from the University of Calcutta in 1919 for his thesis on this topic. Mitra then went to France to continue his studies at the University of Paris. There he earned a second doctorate under Charles Fabry in 1923, for a thesis on the determination of wavelength standards in the 2,000–2,300 Å region of copper. He also worked at the Institute of Physics at the University of Nancy, where he studied the behaviour of thermionic valves and radio frequency oscillations in discharge tubes. It was during this period that he developed an interest in radio wave propagation and decided to pursue this line of research. In 1923, Mitra returned to India and took up the Khaira Chair of Physics at the University of Calcutta. He established the first course on wireless technology in India and set up a laboratory for radio physics research. He also initiated studies on atmospheric electricity and solar radiation. He soon became a leading authority on ionospheric physics, which deals with the study of the ionized layer of the upper atmosphere that affects radio wave transmission. He conducted extensive experiments on ionospheric phenomena such as absorption, reflection, refraction, polarization, fading, and scintillation of radio waves. He also investigated the effects of solar flares, geomagnetic storms, auroras, meteors, and cosmic rays on the ionosphere. Mitra made several original contributions to ionospheric science, such as discovering new layers in the ionosphere (the E2 layer and the F2 layer), explaining the mechanism of night airglow (the faint emission of light by atoms and molecules in the upper atmosphere), developing methods for measuring ionospheric parameters (such as electron density, height, and temperature), and proposing theories for the formation and variation of the ionosphere. He also devised techniques for improving radio communication and navigation, such as using multiple frequencies, directional antennas, and ionospheric sounding. He published over 200 papers and several books on his research work. Mitra was also actively involved in the administration and promotion of science in India. He served as the head of the Department of Physics and the Dean of the Faculty of Science at the University of Calcutta. He was instrumental in establishing the Institute of Radio Physics and Electronics, the S.N. Bose National Centre for Basic Sciences, and the Indian Association for the Cultivation of Science in Kolkata. He was also associated with various scientific institutions and societies, such as the Indian National Science Academy, the Indian Physical Society, the Asiatic Society of Bengal, and the National Institute of Sciences of India. He was a member of several national and international committees and commissions on radio science, atmospheric science, and meteorology. Mitra received many honours and awards for his scientific achievements, such as the Fellow of the Royal Society of London (1956), the Padma Bhushan (1962), the National Professorship (1962), and several honorary doctorates from Indian and foreign universities. He also had a lunar crater named after him by the International Astronomical Union. Mitra was married to Lilavati Biswas, a social worker and a freedom fighter, in 1914. They had two sons and a daughter. Mitra died on 13 August 1963 in Kolkata after a short illness. He is remembered as one of the most eminent physicists of India and a pioneer of ionospheric science.