Sisir Kumar Mitra — Indian physicist with a crater named after him on moon

On 26 August, ISRO released a set of pictures in which crater 'Mitra', named after physicist Sisir Kumar Mitra, can be seen.

Mitra crater on the moon; Radio physicist Sisir Kumar Mitra (inset) | Background image: Twitter @isro | Inset image: insa.nic.in

Bengaluru: On 26 August, the camera of Chandrayaan-2’s orbiter had zeroed in on a crater named after 20th century scientist Sisir Kumar Mitra — a leading Indian physicist who helped establish the first radio science course at the Calcutta University.

Images of crater ‘Mitra’, in the moon’s northern region, are among the second set of photographs released by the Indian Space Research Organisation (ISRO).

An ionosphere expert, Mitra had established the first-ever course to study wireless technology in India at the Calcutta University. He also set up the first ionospheric field station at Haringhata near Kolkata in 1950.

The acclaimed radio physicist is most well known for his treatise The Upper Atmosphere (1947) — which details his contributions to the field of ionospheric studies. The treatise went on to be internationally recognised and has since been translated into multiple languages.

Mitra was elected a Fellow of the Royal Society, London in 1958 for his contributions to the study of upper atmospheric phenomena. He was awarded the Padma Bhushan in 1962.

Foray into physics

Mitra was born in 1890 at Konnagar, a suburb of Kolkata located in the then Bengal Presidency. While his mother was a doctor, Mitra’s father was a school teacher.

He first heard about Ram Chandra Chatterjee — an acrobat, balloonist and parachutist  — when he was about six-seven years old and went on to develop a keen interest in spaceflight. Chatterjee had, in 1889, become the first Indian aeronaut to do a solo flight on a balloon.

Mitra also read popular writings on science by renowned Bengali scientists, including Jagadish Chandra Bose.

He pursued a B.Sc and an M.Sc in physics from the Presidency College in Kolkata in 1912 and later worked as a research scholar under Jagadish Chandra Bose. Mitra, however, could not pursue his PhD due to increasing financial difficulties, especially after the death of his father and two brothers.

To support his mother, brother and a sister, Mitra started teaching at his alma mater, TNJ College and then at the Bankura Christian College in West Bengal.

But the lack of research opportunities frustrated him, and Mitra resorted to pursuing innovative experiments for students and writing for science magazines.

In 1916, he was invited to work as a post-graduate research scholar in physics under the guidance of C.V. Raman.

Moving to Paris

Mitra worked with Raman on light diffraction. At 26, he was already a lecturer at the department of physics in University College of Science in Calcutta University. He also received his doctorate from the varsity in 1919, in just three years.

Mitra moved to the University of Paris to work on his second doctorate on copper wavelength standards. Here, he worked under Charles Fabry, a light interference expert who had studied the upper atmosphere. Fabry was also the co-discoverer of the ozone layer of the earth, which exists in the upper atmosphere.

He also worked under Marie Curie for a short period of time at the Radium Institute (now Curie Institute) in Paris before deciding to study the new and emerging concept of radio communications. Mitra went to the University of Nancy in France later to work under Camille Gutton, who helped develop the radar and was a leading authority in radio electricity.

Returning to India

In 1923, Mitra decided to return to India. He was already in touch with Ashutosh Mukherjee, the famed educator and vice-chancellor of Calcutta University who had first invited Mitra to work under Raman.

He reached out to Mukherjee again and told the latter about the growing relevance of wireless communication. Mitra explained to Mukherjee the need for establishing wireless science as a field of study for post-graduate students.

Mukherjee finally established the course in Calcutta University and Mitra became professor of physics. He also became part of a team of leading physicists who were responsible for shaping post-graduate research in physics.

He was tasked with establishing research on wireless communication in India. A wireless laboratory was subsequently set-up and the course eventually expanded to a new department before becoming a specialised Institute of Radio Physics and Electronics.

Study of the ionosphere is also closely tied with radio research. Ionosphere is a region of the upper atmosphere, nearly 75-1,000 km above Earth’s surface. In this band of air, atoms and molecules are ionised by solar radiation. While ions conduct electricity, they also enable communication by reflecting radio waves around Earth.

Mitra’s new laboratory had built an instrument that could measure heights in the different parts of the ionosphere. The results obtained from his research had provided the first insight into ionospheric conditions in sub-tropical regions and effects on atmospheric ionisation due to natural phenomena such as lightning and meteor showers.

While working here, Mitra also contributed to the development of radio broadcasting. The Radio Club of Bengal was the first to start a broadcast of regular programmes. And for a long time, Mitra’s laboratory and the Bengal Radio Club were the only broadcasters for the entire eastern region.

A company named Indian States and Eastern Agency later installed India’s first radio broadcast transmitter in Kolkata in 1923 and the Indian Broadcasting Company was finally established in 1927.

In the meanwhile, Mitra also pushed for more ionospheric research. With funding from the Council of Scientific and Industrial Research (CSIR), Mitra established a field station at Haringhata, about 50km from Kolkata. It was the first ionosphere field station in India and studied this part of the atmosphere 24-hour a day.

False leads

Mitra had falsely believed that the night sky’s glow was caused by neutralisation of ions and electrons in the upper atmosphere. His theories were never accepted due to lack of observational data to support them.

He later went on to establish the Radio Research Committee with help from Meghnad Saha. Mitra also established industrial schemes, such as indigenous production of microphones and loudspeakers, as well as production of electron tubes. This resulted in production of radio valves in India for the first time.

He retired in 1955 and joined the West Bengal Secondary Education Board. He was also a founding member of the National Institute of Science (later renamed as Indian National Science Academy) and became its president in 1956.

Mitra was working on publishing a third edition of his famed treatise The Upper Atmosphere but passed away on 13 August 1963 after a brief illness.