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Meghnad Saha
A Pioneer in Astrophysics
Dr Subodh Mahanti
“The impetus given to astrophysics by Saha’s work can scarcely be overestimated, as nearly all later progress in this field has been influenced by it and much of the subsequent work has the character of refinements of Saha’s ideas.”
S. Rosseland in Theoretical Astrophysics (Oxford University Press, 1939)

“Scientists are often accused of living in the “Ivory Tower” and not troubling their mind with realities and apart from my association with political movements in my juvenile years, I had lived in ivory tower up to 1930. But science and technology are as important for administration now-a-days as law and order. I have gradually glided into politics because I wanted to be of some use to the country in my own humble way.”

Meghnad Saha

“He (Saha) was extremely simple, almost austere, in his habits and personal needs. Outwardly, he sometimes gave an impression of being remote, matter of fact, and even harsh, but once the outer shell was broken, one invariably found in him a person of extreme warmth, deep humanity, sympathy and understanding; and though almost altogether unmindful of his own personal comforts, he was extremely solicitous in the case of others. It was not in his nature to placate others. He was a man of undaunted spirit, resolute determination, untiring energy and dedication.”

D. S. Kothari in Biographical Memoirs of Fellows of the National Institute of Sciences of India, Vol .2, New Delhi, 1970

‘Meghnad Saha’s place in the history of astrophysics and in the history of modern science in India is unique’, wrote Subrahmanyan Chandrasekhar (1910-95). Saha’s theory of thermal ionisaiton, which explained the origin of stellar spectra, was one of India’s most important contributions to world science during the 20th century. It was an epoch-making discovery. Arthur Stanley Eddington (1882-1944), while writing on stars in the Encyclopaedia Britannica, described Saha’s theory of thermal ionisaiton as the twelfth most important landmark in the history of astronomy since the first variable star (Mira Ceti) discovered by Saha made important contributions in different branches of physics. Saha (jointly with B.N. Srivastava) wrote the renowned textbook, entitled, Treatise on Heat, which was originally published in 1931 under the title, A Text Book on Heat. It was Saha who first started the teaching and training in nuclear physics in the country. The first cyclotron in the country was built with Saha’s initiatives. Saha was a great institution builder. Among the institutions that he built were: National Academy of Sciences, India, at Allahabad, Indian Physical Society, Kolkata, National Institution of Sciences of India (which was later renamed Indian
National Science Academy), New Delhi, Indian Science News Association, Kolkata, and Saha Institute of Nuclear Physics, Kolkata. Saha was an active member of the National Planning Committee constituted by the Indian National Congress in 1938 with Jawaharlal Nehru as its Chairman. He was the Chairman of the Indian Calendar Reform Committee constituted by the Council of Scientific and Industrial Research in 1952. He was an elected Independent Member of the Indian Parliament. He advocated large-scale industrialisation for social development.

Meghnad Saha was born on October 06, 1893 in the village of Seoratali in the Dhaka (then Dacca) district (now in Bangladesh) of undivided India. He was the fifth child of his parents, Jagannath Saha and Bhubaneswari Devi. His father, Jagannath, was a petty shopkeeper. Given their social and economic background his parents had neither the means nor the inclination for educating their children beyond the primary education. Saha’s elder brother Jainath, after failing to pass the matriculation examination, started working in a jute company on a monthly salary of Rs.20. His second brother had to discontinue his school education in order to help his father in running the shop. At the age of seven Saha joined the village primary school and from the very beginning he demonstrated an unusual aptitude for learning.

Radharani Saha, wife of Saha,

After the completion of his primary education there was no certainty that his education would continue further. Their parents would have preferred to have him work in the family’s grocery shop. In any case they did not see any use of further education in running the shop. Moreover there was no middle school nearer to his village. The nearest middle school was at Simulia, which was 10 kms away from his village. Saha’s parents did not have the means to take care of the expenses of his boarding and lodging. At this stage his elder brother Jainath came in his rescue by locating a sponsor in Ananta Kumar Das, a local doctor. The kind-hearted doctor agreed to provide Saha free boarding and lodging in his house provided Saha washed his own plates (a condition that reflected the prevailing rigid caste system) and attend minor household works including the taking care of the cow. Saha readily accepted all the conditions as he had a strong urge to continue his studies further. Every weekend he used to visit his village. When the village became flooded he would row all the way, otherwise he would simply walk down. Saha completed his middle school by topping the list of successful candidates in the entire district of Dhaka. As a result he secured a scholarship of Rs.4 per month. In 1905 Saha came to Dhaka, where he joined the Collegiate School, a government school. His elder brother sent him a monthly allowance of Rs.5, it was indeed a great sacrifice on his part, as his total monthly salary was Rs.20. The Purba Banga Baisya Samiti gave another Rs.2 per month. So Saha had Rs.11 to manage his food, lodging and other expenses.

There were widespread political disturbances in Bengal in 1905. In this year Lord Curzon, the then Viceroy of British India, had decided to partition Bengal. Saha, like many others, was affected by this political upheaval. He, along with some other students, were rusticated from the Collegiate School, because of their participation in the demonstration against the visit of the Bengal Governor, Sir Bamfylde Fuller, to the school. It is not certain whether Saha actually participated in the demonstration or not, because there is another version of the story. According to this version, Saha did not take part in the demonstration. On that fateful day as usual he had gone to school barefooted. For Saha it was a usual practice, as he had not enough money to buy shoes. But on that day the authorities took it as a deliberate insult directed against the Governor. Besides being rusticated Saha was deprived of his scholarship. Fortunately a private school, named Kishori Lal Jubilee School, accepted Saha with a free studentship and a stipend. In 1909 Saha passed the Entrance Examination from Kishori Lal Jubilee School standing first amongst all the candidates from erstwhile East Bengal.

In school Saha’s favourite subject was mathematics and he also liked history. He was particularly fond of reading Todd’s Rajasthan. He used to be fascinated by the heroic tales of Rajput and Maratha warriors. Among his favourite books were Rabindranath Tagore’s Katha O Kahini, which glorifies the values of the Rajput and Maratha warriors and Madhusudan Dutt’s epic poem Meghnad Badh. During his school days Saha also attended the free Bible classes conducted by the Dhaka Baptist Mission. He stood first in one of the competitive examinations of Bible conducted by the Mission and received a cash prize of Rs.100.

After passing the Intermediate Examination of the Calcutta University in 1911 from the Dhaka College, Dhaka, Saha joined the Presidency College at Kolkata (then Calcutta). Among his classmates was Satyendranath Bose, of the Bose-Einstein Statistics fame. Prasanta Chandra Mohalanobis, the founder of the Indian Statistical Institute, was his senior by a year. His teachers included Prafulla Chandra Ray in chemistry and Jagadis Chandra Bose in physics. Saha passed his BSc Examination with Honours in Mathematics in 1913 and MSc (Applied Mathematics) Examination in 1915. Saha stood second in order of merit in both the examinations. The first position in both cases went to S.N. Bose.

With President Rajendra Prasad

Saha was appointed lecturer in the Department of Applied Mathematics in 1916 in the University College of Science. The foundation stone of the University College of Science was laid down on 27 March 1914 just four days before Asutosh Mookerjee laid down his office as Vice Chancellor of the University. It may be noted here that Mookerjee who was the Vice Chancellor of the Calcutta University during 1906-14 and then again during 1921-23. Both Saha and S.N. Bose, who also joined the Department as a lecturer, got themselves transferred to the Physics Department, where a year later C.V. Raman joined as Palit Professor of Physics. After joining the physics department Saha started giving lectures to the post-graduate classes on topics like hydrostatics, the figure of the Earth, spectroscopy and thermodynamics. For teaching physics to the postgraduate classes, Saha had to learn it himself first, as he studied physics only in the undergraduate classes. It was a great challenge indeed. Besides teaching Saha also started doing research. It was not an easy task. In those days there was no experimental laboratory in the Department of Physics of the University College of Science. He had only one ‘research facility’ that is the wellequipped Library of the Presidency College. Saha had no guide for supervising his research work. He totally depended on his knowledge acquired from private studies. During this period Saha did not have enough money to pay for publication of his research paper in foreign journal. To quote Saha :

“By the end of 1917, I had written a long essay on `Selective Radiation Pressure’ elaborating on theory of the role of radiation pressure’ acting on the atom selectively and compensating the action of gravity on solar atoms. This paper was sent to the Astrophysical Journal for publication, but the editors replied that as the paper was rather long, it could be published only if I were willing to bear a part of the printing costs which ran to three figures in dollars. Much as I would have liked to do so, it was not possible me to find out so much money as my salary was small and I had to maintain my old parents and a younger brother who was studying within this salary. So I wrote to the editors of the Astrophysical Journal expressing my inability to pay the costs of printing, but never heard anything more about the publication of this paper nor was it returned to me. Years afterwards, in 1936, when I visited Yerkes Observatory, Dr. Morgan showed me the manuscript which was still being kept there. I got a short note published in the Astrophysical Journal, Vol. 50,220 (1919) and submitted a duplicate of the original article on `selective radiation pressure and problem of solar atmosphere’ ( Journal of the Department of Science, Calcutta University, 1919) sometime afterwards for publication in our own university journal which had no circulation worth mentioning. I am mentioning these facts because I might claim to be the originator of the Theory of Selective Radiation Pressure, though an account of above discouraging circumstances, I did not pursue the idea to develop it. E.A. Milne apparently read a note of mine in Nature 107, 489 (1921) because in his first paper on the subject `Astrophysical Determination of Average of an Excited Calcium Atom, in Month. Not. R. Ast. Soc., Vol.84, he mentioned my contribution in a footnote, though nobody appears to have noticed. His exact words are: `These Paragraphs develop ideas originally put forward by Saha’.”

Initially Saha worked on diverse topics as reflected from the titles of his published research papers as indicated below:

  • “On Maxwell’s Stresses” ( Philosophical Magazine, 1917), this paper was based on his studies of the electromagnetic theory of radiation;
  • “On the Limit of Interference in the Fabry-Perot Interferometer” ( Physical Review, 1917),