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Biographical Memoirs :: MEGHNAD SAHA

Saha's early lectures to the post-graduate classes covered diverse subjects such as hydrostatics, the figure of the earth, spectroscopy, and thermodynamics; and he was in charge of the Heat Laboratory. Many of the subjects were new to him - he had taken physics in the undergraduate classes only - but this only served to stimulate his dauntless spirit all the more, and he studied the new subjects, specially thermodynamics and spectroscopy, with great avidity and zest. It was fortunate, as he often recalled in later life, that about a year earlier he had come across Miss Agnes Clerke's two popular books on the sun and the stars.

These books fascinated him greatly and gave him some idea of the main problems in astrophysics. He now read, amongst other books, Planck's Thermodynamics and Nernst's Das Neue Warmesätz, and he was familiar with the papers of Bohr and also Sommerfeld on the quantum theory of the atom. All this in a sense paved the way for his epochal work on the thermal ionization of elements. More will be said about this presently.

Shortly after the end of the First World War there was announced the momentous discovery of the deflexion of starlight by the gravitational field of the sun, confirming Einstein's theory of general relativity. Saha got deeply interested in the relativity theory. He, jointly with S. N. Bose, prepared an English translation of Einstein's papers, later published in the form of a book by the University of Calcutta. The study of relativity led Saha to some investigations in electromagnetic theory and his first original paper entitled `On Maxwell's stresses' appeared in the Philosophical Magazine in 1917. This was followed by papers on the dynamics of the electron. He derived, on the basis of the special theory of relativity, the Lienard-Wiechert potential due to a point-charge. During these years he also worked on radiation pressure, and in 1918 (with S. Chakravorti) he published in the Journal of the Royal Asiatic Society of Bengal (Calcutta) a paper on the measurement of the pressure of light, using a resonance method. Though Saha had little real skill or aptitude for practical work, he always took the keenest interest in and gave every encouragement to experimental work going on in his laboratory, and often suggested fruitful problems for investigation. He held that in a progressive department of physics, research should be vigorously pursued in both theory and experiment, and a high place given to serious and good teaching. Saha's first work in astrophysics, and it was a very important one, was the formulation of the concept of selective radiation pressure, and the recognition of its role in the relative distribution of the elements in the solar atmosphere. (He had read in Agnes Clerke's book about the `hypothetical levitative force' which apparently acted on atoms of some elements only, e.g. calcium.) A short note `On radiation pressure and the quantum theory' appeared in the Astrophysical Journal in 1919. A detailed paper communicated to the same journal was for some reasons - partly the length of the paper - not accepted for publication, and it was published in the relatively little known Journal of the Department of Science, Calcutta University. Saha did not pursue the subject of selective radiation pressure further. It was raised to an entirely new level by E. A. Milne. In 1918 on the basis of his work in the field of electromagnetic theory and radiation pressure, Saha was awarded the D.Sc. degree of the Calcutta University. His examiners were O. W. Richardson, N. R. Campbell and Porter.

Biographical Memoirs :: MEGHNAD SAHA

Saha's greatest contribution is, undoubtedly, the theory of high - temperature ionization and its application to stellar atmospheres. The equation that goes by his name was first given in the paper `On ionization in the solar chromosphere', published in the Philosophical Magazine for October 1920. Using the language of physical chemistry he called it the `equation of the reaction-isobar for ionization'.

Discussing the case of the ionization of calcium, he wrote:

`We may regard the ionization of calcium atom as taking place according to the following scheme, familiar in physical chemistry,
                                           

where Ca is the normal atom of calcium (in the vapour state), Ca+ is an atom which has lost one electron, U is the quantity of energy liberated in the process. The quantity considered, is 1 g atom ... To calculate the "Reaction-isobar" K, let us assume that P is the total pressure, and a fraction x of the Ca-atom is ionized.

Then we have
               

This is the equation of the "reaction-isobar" which is throughout employed for calculating the "electron-affinity" of the ionized atom.' The value 6.5 in the above expression is the value of the Chemical constant obtained from the Sackur-Tetrode-Stern relation.

It is pertinent to remark that the ionization theory was formulated by Saha, working by himself in Calcutta, and the paper quoted above was communicated by him from Calcutta to the Philosophical Magazine -- incorrectly, statements to the contrary have sometimes been made. (Saha's first visit to Europe was made a couple of months later. ) Further papers soon followed. It is not too much to say that the theory of thermal ionization introduced a new epoch in astrophysics by providing for the first time, on the basis of simple thermodynamic considerations and elementary concepts of the quantum theory, a straightforward interpretation of the different classes of stellar spectra in terms of the physical conditions (temperature and to a lesser extent pressure) prevailing in the stellar atmospheres. S. Rosseland in the Introduction to his well-known `Theoretical astrophysics' (Oxford University Press, 1936) has observed: `Although Bohr must thus be considered the pioneer in the field, it was the Indian physicist Meghnad Saha who (1920) first attempted to develop a consistent theory of the spectral sequence of the stars from the point of view of atomic theory. Saha's work is in fact the theoretical formulation of Lockyer's view along modern lines, and from that time the idea that the spectral sequence indicates a progressive transmutation of the elements has been definitely abandoned. From that time dates the hope that a thorough analysis of stellar spectra will afford complete information about the state of the stellar atmospheres, not only as regards the chemical composition, but also as regards the temperature and various deviations from a state of thermal equilibrium, the density distribution of the various elements, the value of gravity in the atmosphere and its state of motion. 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.'

Biographical Memoirs :: MEGHNAD SAHA

It may be of some interest to relate how Saha was led to the ionization theory. In his own words1 : `It was while pondering over the problems of astrophysics, and teaching thermodynamics and spectroscopy to the M.Sc. classes that the theory of thermal ionization took a definite shape in my mind in 1919. I was a regular reader of German journals, which had just started coming after four years of First World War , and in course of these studies, I came across a paper by J. Eggert in the `Physikalische Zeitschrift' (p. 573), Dec. 1919, "Uber den Dissoziationzustand der Fixsterngase" in which he applied Nernst's Heat Theorem to explain the high ionization in stars due to high temperatures, postulated by Eddington in course of his studies on stellar structures.2

`Eggert, who was a pupil of Nernst and was at the time his assistant, had given a formula for thermal ionization, but it is rather strange that he missed the significance of ionization potential of atoms, importance of which was apparent from the theoretical work of Bohr, and practical work of Franck and Hertz, which was attracting a good deal of attention in those days. ... Eggert used Sackur's formula of the chemical constant for calculating that of the electron, but in trying to account for multiple ionization of iron atoms in the interior of stars on this basis, he used very artificial values of ionization potential.

`While reading Eggert's paper I saw at once the importance of introducing the value of "ionization potential" in the formula of Eggert, for calculating accurately - the ionization, single or multiple, of any particular element under any combination of temperature and pressure.

`I thus arrived at the formula which now goes by my name. Owing to my previous acquaintance with chromospheric and stellar problems, I could at once see its application. I prepared in the course of six months of 1919 (February to September) four papers and communicated them for publication in the Philosophical Magazine from India within August to September.

One of the four papers above referred to was `On the Harvard classification of stellar spectra'. When shortly after communicating the paper Saha went to London, he withdrew it from the Philosophical Magazine, and completely rewrote it in Professor A. Fowler's spectroscopy laboratory in the Imperial College of Science and Technology, London. The revised (and, no doubt, considerably expanded and improved) paper was published in the Proceedings of the Royal Society ( 1921) under the title, suggested by Fowler , `On a physical theory of stellar spectra'. Saha had the greatest regard for Professor Fowler, and always spoke with warmth and gratefulness of the encouragement and help he had received from him in London. Years after wards he wrote3 : `I took about four months in rewriting this paper, and all the time I had the advantage of Professor Fowler's criticism, and access to his unrivalled stock of knowledge of spectroscopy and astrophysics. Though the main ideas and working of the paper remained unchanged, the substance matter was greatly improved on account of Fowler's kindness in placing at my disposal fresh data, and offering criticism wherever I went a little astray, out of mere enthusiasm.'4 This paper and the one on the `Ionization of the solar chromosphere' are by far the most significant and original of Saha's many scientific contributions.

1 Extract (taken from a copy in the possession of Dr A. K, Saha, son of Professor Saha) from a letter dated 18 December 1946, to Professor H. H. Plaskett, University Observatory, Oxford.

2 Saha in his paper `On ionization in the solar chromosphere' makes a handsome acknowledgment to Eggert's work.

3 Letter to Professor H. H. Plaskett referred to in the preceding footnote.

4 Professor H. Dingle once observed : `On thinking back to the relation which existed between Saha and Fowler I am tempted to compare it, with that between Maxwell and Faraday'. ( The Observatory 66, 22 (1945).)

Biographical Memoirs :: MEGHNAD SAHA

As one of the interesting and immediate results following from the ionization theory, Saha not only was able to explain the absence in the solar spectrum of the lines of Rb and Cs because of the low ionization potential of these elements, but also to predict that their resonance lines were likely to be observed in the relatively cooler region of the sunspots. H. N. Russell, following Saha's prediction, looked for and found the infra-red pair of Rb-lines, but no Cs-lines, in the Mount Wilson photographs of the spot spectra which, incidentally, had been taken before the publication of Saha's theory.

We may recall at this place that, apart from J. Eggert's paper referred to earlier, a definite suggestion about high-temperature ionization, prior to Saha's papers, was also made by the Oxford Physicist F. A. Lindemann (later Lord Cherwell) in connexion with his controversy with S. Chapman about the origin of magnetic storms (Philosophical Magazine, December 1919). He gave the ionization formula for hydrogen, and discussed the possibility of the complete ionization of hydrogen in the solar chromosphere. Lindemann, however, did not further develop or generalize the formula; and above all he failed to notice that the theory of thermal ionization (with accurate values of ionization potentials obtained from spectroscopic data or otherwise) constitutes the key to the interpretation of stellar spectra with their almost bewildering complexity. It was Saha who first recognized this, and worked out the consequences in considerable detail, and he did this independently of Lindemann's suggestion about the high-temperature ionization of hydrogen.

In 1919 Saha was Awarded the Premchand Roychand Scholarship of the Calcutta University, and this made it possible for him to spend some two years in Europe. He first went to London and spent about five months in the laboratory of Professor A. Fowler. Later he moved to W. Nernst's laboratory in Berlin, and did some experimental work on the conductivity or heated caesium vapour to seek an experimental verification of the theory of thermal ionization. The results were inconclusive. Some years later, when at Allahabad, Saha again returned to this problem, and an account of the investigation, jointly with K. Majumdar and N. K. Sur, was published in the `Zeitschrift fur Physik' ( 1926) .

Biographical Memoirs :: MEGHNAD SAHA

In the early twenties R. H. Fowler (in collaboration with C. G. Darwin) developed a very powerful method in statistical mechanics permitting a systematic exposition and working out of the equilibrium properties of matter. He used this to provide a (rigorous) derivation of the ionization formula which as described earlier Saha had obtained by extending (and justifiably) to ionization of atoms the theorem of van't Hoff, well known in physical chemistry for its application to molecular dissociation. Also, a significant improvement in the Saha equation introduced by Fowler was to include the effect of the excited states of atoms and ions. Further, it marked an important step forward when in 1923 E. A. Milne and R. H. Fowler in a paper in the Monthly Notices of the Royal Astronomical Society showed that the criterion of the maximum intensity of absorption lines (belonging to subordinate series of a neutral atom) was much more fruitful in giving information about physical parameters of stellar atmospheres than the criterion employed by Saha which consisted in the marginal appearance or disappearance of absorption lines. (The latter criterion requires some knowledge of the relevant pressures in the stellar atmospheres, and Saha following the generally accepted view at the time assumed a value of the order of 1 to 0.1 atmosphere.) To quote from E. A.Milne5 : `Saha had concentrated on the marginal appearances and disappearances of absorption lines in the stellar sequence, assuming an order of magnitude for the pressure in a stellar atmosphere and calculating the temperature where increasing ionization, for example, inhibited further absorption of the line in question owing to the loss of the series electron. As Fowler and I were one day stamping round my rooms in Trinity and discussing this, it suddenly occurred to me that the maximum intensity of the Balmer lines of hydrogen, for example, was readily explained by the consideration that at the lower temperatures there were too few excited atoms to give appreciable absorption, whilst at the higher temperatures there are too few neutral atoms left to give any absorption. ..That evening I did a hasty order of magnitude calculation of the effect and found that to agree with a temperature of 10000o for the stars of type AO, where the Balmer lines have their maximum, a pressure of the order of 10-4 atmosphere was required. This was very exciting, because standard determinations of pressures in stellar atmospheres from line shifts and line widths had been supposed to indicate a pressure of the order of one atmosphere or more, and I had begun on other grounds to disbelieve this.'

In November 1921 Saha returned from Europe and joined the University of Calcutta as Khaira Professor of Physics, a new chair created from the endowment of Kumar Guruprasad Singh of Khaira. In 1923 Saha left Calcutta to take up the appointment of Professor and Head of the Physics Department in the University of Allahabad. He held this appointment for 15 years. At Allahabad he gave a large part of his time to teaching - he regularly lectured to undergraduate and postgraduate classes. His lectures were systematically and carefully prepared, and a very large part of what he spoke, he wrote on the blackboard in his characteristically clear and bold handwriting. He made copious use of lantern slides, and was fond of demonstration experiments6.

5 E.A.Milne, Obituary Notice of R. H. Fowler (1889-1944), Obituary Notices of the Fellows of the Royal Society, 5, 61-78 (1945)

6 Saha quoted the following rather remarkable passage from the 9th century Sanskrit work , Rasendra Chintamani: "I have much from the lips of savants, I have seen many (formulae) well established in Scriptures, but I am not recording any which I have not done myself.
"I am only recording those fearlessly, which I have carried out before my elders, with my own hand. They are alone to be regarded as real teachers ,who can show by experiments what they teach. They are observing pupils, who, having learnt from their teachers can actually perform them and improve upon them. The rest are merely stage-actors."

Biographical Memoirs :: MEGHNAD SAHA

He initiated and organized research in several subjects, such as statistical mechanics, atomic and molecular spectroscopy, experiments on thermal ionization and `electron affinity' of electronegative elements, active modification of nitrogen, high-temperature dissociation of molecules, and ionospheric propagation of radio waves and physics of the upper atmosphere. In 1926 Saha presided at the Physics and Mathematics Section of the Indian Science Congress Association. His address was on thermal ionization. Within less than a decade of Saha's arrival the Physics Department of the Allahabad University became one of the most active centres of research in the country, particularly in the field of spectroscopy. Amongst his earliest associates in research mention may be made of P. K. Kichlu (now Professor of Physics in the Delhi University), K. Majumdar and N. K. Sur. The Department attracted students from all over India. R. C. Majumdar, now Professor of Physics in the Delhi University, S. Basu, the present Director-General of the Department of Meteorology, and D. S. Kothari were Saha's students at Allahabad. It was in 1927 that at the age of thirty-four Saha was elected to the Royal Society. The United Provinces Government sanctioned a personal annual grant of Rs. 5000 for his research work.

In 1927, at the invitation of the Italian Government, Saha attended the Volta Centenary Celebration held at Como, and presented a paper `On the explanation of complicated spectra of elements'. He later joined a total solar eclipse expedition to Ringebu (68^ N) led by L. Vegard of Oslo University. In 1936 he was elected to an overseas fellowship of the Carnegie Trust of the British Empire, and he visited Germany, England, and the United States and spent about two months with H. Shapley at the Harvard College Observatory. (Saha took keen interest in archaeology and ancient history, and on his way to Europe he visited the ruins of Ur of the Chaldecs then recently excavated by Sir Leonard Woolley.) In a paper `On a stratospheric astrophysical observatory' which appeared in the Records of Harvard College Observatory, Saha made what at the time (1936) was a very ambitious plea of photographing the solar spectrum at a height of some 50 kilometres, well above the ozone layer; and he pointed out the enormous gain that would accrue for astrophysics. In this paper, as also in that on the action of ultraviolet sunlight upon the upper atmosphere published in the Proceedings of the Royal Society (1937) and in his Presidential Address to the National Institute of Sciences of India given at Lahore in 1938, he discussed the possibility that the ultra-violet radiation from the sun may be several orders of magnitude above that corresponding to a black-body at about 6500 K. He wrote: `This may possibly be due to the fact that the ultraviolet spectrum of the sun may consist of a continuous background of faint light on which are superposed emission lines of H, He, He+, Fe+, and other elements which are represented in the visible range by lines of subordinate series, or by patches of ultra-violet continuous light (near about ? 500) leaking through the solar atmosphere from a much hotter region inside the photosphere, as suggested by Professor H. N. Russell.`7

7 M.N. Saha. Proc.Roy. Soc. A, 160, 55 (1937).

Biographical Memoirs :: MEGHNAD SAHA

In December 1937, Sir Arthur Eddington visited India as a member of the delegation of the British Association for the Advancement of Science to the Jubilee Session (1938) of the Indian Science Congress Association held in Calcutta. (Lord Rutherford was to preside at the session but he died a few months before, and his place was taken by Sir James Jeans.) At Saha's invitation Eddington paid a short but memorable visit to Allahabad; he was presented a civic address by the Allahabad Municipality.

In 1938 Saha was offered the Palit Chair in Physics at the University of Calcutta, vacated some years earlier by C. V. Raman who had gone to Bangalore as Director of the Indian Institute of Science. (Raman was succeeded by D. M. Bose who was Palit Professor from 1932 to 1937.) Saha accepted the offer and left Allahabad after a stay of fifteen years there. He occupied the Palit Chair for fifteen years, retiring in 1953 at the age of 60. In Calcutta Saha could not give as much of his time to his research as was possible in the relatively quiet atmosphere of Allahabad. Here a large part of his time was taken up in the administration of the laboratories, in building a new Institute of Nuclear Physics, and the reorganization and expansion of the laboratories of the Indian Association for the Cultivation of Science. Apart from all this, after the partition of India in 1947, he gave a substantial part of his time and energy to the massive human and economic problem of the `refugees' from East Bengal (Pakistan) - it was a call that a man, himself from East Bengal, of his temperament and intense sensibility could not resist.

His researches in Calcutta were concerned largely with the systematics of atomic nuclei, particularly beta-activity; the propagation of electromagnetic waves in the ionosphere; and the problem of the solar corona. In the case of the corona an outstanding problem is that of the mechanism or source responsible for the high-degree ionization - loss of 9 to 13 electrons - of the iron atoms, and also nickel in the inner corona, as conclusively demonstrated by B. Edlen's remarkable work (1938) on the origin of the coronal bright spectral lines. D. Kundu working under Saha showed that some of the lines may be due to highly ionized cobalt atoms. The intense ionization, as also the excessive broadening of the Fraunhofer lines in the scattered radiation from the outer corona, and the strong coronal radio-emission in the region of wavelengths of the order of a few metres, all suggest coronal temperatures of the order of millions of degrees, but the origin of these temperatures which are comparable to those occurring in stellar interiors is largely still an unsolved problem. Saha found it difficult to accept the existence of such high temperatures. In fact, to account for the Edlen lines he advanced in a number of papers the somewhat quaint hypothesis that the highly charged ions necessary for the emission are produced as a result of some form of nuclear fission occurring in the sun's outer atmosphere -- he suggested tri- or quadri-fission of U or Th. The problem of the emission of radio waves from the sun and other stellar bodies also engaged his attention, and he discussed the likely role of the magnetic field and the hyperfine-structure level-splitting of the ground state of the H-atom (Nature, Lond. 158, 717 (1946)). He failed to recognize, at any rate explicitly, the possibility of the occurrence as line emission of the 21-cm hydrogen line in radio spectra. (He was not aware at the time of the earlier prediction (1944) of H. C. van de Hulst.) In collaboration with B. D. Nag Chaudhuri (the present Palit Professor of Physics) Saha investigated the problem of the geological age of some of the Indian rocks.

Biographical Memoirs :: MEGHNAD SAHA

Saha early realized the growing importance of nuclear physics and the impact it was likely to make on the country's scientific and industrial progress. He felt that in the context of current developments there was a real and urgent need for a separate institution of nuclear physics devoted to post-graduate study and research. The result of his dedicated and untiring efforts was the Institute of Nuclear Physics in Calcutta, founded in April 1948 (and formally opened in 1950). The Institute is attached to the University. It runs a post-graduate course, and its research activities cover, amongst other subjects, beta-ray spectroscopy, nuclear resonance, and the use of radioactive isotopes in medicine. There is also an active theoretical group; a separate biophysics section and an instrument section. It has a 38-inch cyclotron - the magnet and some of the other critical parts were obtained from Lawrence's Laboratory in Berkeley. Saha was elected Honorary Director of the Institute for life. After his death, the Institute befittingly has been named after him.

Though the Institute of Nuclear Physics took much of Saha's energy and time, yet there was another institution, the Indian Association for the Cultivation of Science, which was always in his mind, and for its reorganization and expansion he worked hard and ceaselessly. The Association, the oldest institution devoted to science and its cultivation in modern India, was founded in 1876 by a private medical practitioner of Calcutta, Dr Mahendra Lal Sircar. He intended it `to combine the character, scope and objects of the Royal Institution of London and of the British Association for the Advancement of Science. As is well known the Raman effect was discovered in the laboratories of the Association in 1928. At the time Raman was Palit Professor of the University and also the honorary head of the Laboratories of the Association.

Saha, shortly after his coming to Calcutta as Palit Professor in 1938 (Raman left Calcutta in 1932) began to take a keen interest in the activities of the Association. He was elected the Honorary Secretary in 1944, and in 1946 he was elected the President of the Association. He was succeeded by J. C. Ghosh in 1950. The large-scale expansion in the research activities of the Association which has taken place in recent years is almost entirely the result of Saha's initiative, resourcefulness and devoted work. The Association has now a new building in Jadavpur (Calcutta) where it moved in 1951 from 210 Bowbazar Street.

In 1952 the post of a full-time Director of the Laboratories of the Association was created and the choice of the first Director obviously fell on Saha. He accepted the appointment in 1953 on retirement from the Palit Chair of the University which he held for fifteen years. He was Director of the Laboratories of the Association and Honorary Director of the Institute of Nuclear Physics at the time of his death in 1956. Saha was the General President of the twenty-first annual session of the Indian Science Congress Association held in Bombay in January 1934. The first part of his address dealt with some of the current astrophysical problems, and in the second part he advocated the formation of an All-India Academy of Sciences. In the same address he drew pointed attention to the serious problem - still largely unsolved - of recurring disastrous floods in many Indian rivers, and stressed the need for a River Research Laboratory to make a scientific study of the complex problems involved in flood control and river utilization generally. He was one of the first in India to realize the great importance of this subject. He had personal experience of some of the catastrophic floods in the Damodar Valley area (Bengal), and he often took an active part in relief measures organized to deal with them. The writings of Saha, many of which appeared in Science and Culture, on flood control and harnessing the water of the rivers were to no small extent responsible in creating a public awareness of these problems. In 1943 the Bengal Government appointed the Damodar Flood Enquiry Committee. Saha was a member of the Committee, and his contribution was widely recognized as a vital one. Largely as a result of the committee's report came, eventually, the multipurpose Damodar Valley Project (very much on the lines of the Tennessee Valley Authority in the U.S.A.) which has been the forerunner of the Bhakra-Nangal and other multipurpose river projects in India. The establishment of the River Research Institute (Haringhata, Calcutta) was also, to no small extent, the result of Saha's initiative and efforts.

Biographical Memoirs :: MEGHNAD SAHA

It was during the early thirties that the National Academy of Sciences at Allahabad (originally called the Academy of Sciences for the Provinces of Agra and Oudh), the Indian Academy of Sciences at Bangalore, and the National Institute of Sciences at Calcutta (headquarters transferred to Delhi in 1946) were founded. In the case of the Allahabad Academy, and so also the National Institute, the role of Saha was of the utmost importance. He was the first President ( 1932-34) of the Allahabad Academy and the second President (1937-39) of the National Institute of Sciences. (The first President of the Institute was Sir Lewis Fermor, the Director-General of the Geological Survey of India.) Saha was President of the Royal Asiatic Society of Bengal (now the Asiatic Society) for 1944-46.

Saha from the very beginning was closely associated with the work of the Indian Council of Scientific and Industrial Research (which corresponds to the D.S.I.R. in the U.K.) first constituted in 1942. He was a member of the Governing Body; and was for many years chairman of the Atmospheric Research Committee, and chairman or member of several other research and planning committees of the C.S.I.R. He was closely connected with the planning and establishment of the Central Glass and Ceramics Research Institute at Calcutta -- one of the national laboratories under the C.S.I.R. -- and was for many years chairman of its Advisory Committee. He was the chairman of the Indian Calendar Reform Committee, appointed by the C.S.I.R. in 1953.

Saha was a member of the University Education Commission appointed by the Government of India in 1948 under the chairmanship of Dr S. Radhakrishnan.

The monthly journal Science and Culture, published by the Indian Science News Association (Calcutta), was started by Saha in 1934. The journal is now running in its 24th volume. Saha wrote prolifically for the journal, and his many articles and editorials bear witness to his remarkable versatility, and his passionate interest in and grasp of the many scientific, industrial and economic problems facing the country. A list of his contributions is included in the bibliography at the end.

Saha was a keen student and ardent advocate of social and economic planning in India, particularly, in its relation to science, large-scale industry and technology. His general philosophy in these matters is perhaps best expressed in the following words (Nature, Lond. 155, 221 ( 1945) ) : `The philosophy of kindliness and service to our fellow-men was preached by all founders of great religions, and no doubt some great kings and ministers of religions in every country and at all ages tried to give effect to this (altruistic) philosophy. But the efforts were not successful, for the simple reason that the methods of production of commodities were too inefficient to yield plenty for all, which is an indispensable condition for practical altruism. We can, therefore, hold that so far as individual life is concerned, science has achieved a target aimed at by the great founders of religions in advanced countries of the world. The effects or maldistribution or wealth, due to historical causes, are being rapidly cured by the introduction of social laws.'

Biographical Memoirs :: MEGHNAD SAHA

He was an active member of the National Planning Committee appointed by the Indian National Congress in 1938. Saha was chairman or the power and fuels sub-committee, and member of the sub-committee on river training and irrigation.

In 1951 Saha was elected, as an independent candidate, to the Indian Parliament from the North-West Calcutta constituency. His contribution to the debates in the House, because of his special knowledge and background, was particularly valuable in relation to subjects such as education, industrial policy, river-valley projects and atomic energy.

Saha was widely travelled in Europe and the U .S.A. He had been twice to the U.S.S.R. He was the Indian delegate to the 220th Anniversary Celebrations (1945) of the Soviet Academy of Sciences.

In March 1954 the 60th birthday of Saha was celebrated in Calcutta, Allahabad and Delhi by his many friends, old students and admirers. A Commemoration Volume Professor Meghnad Saha - His life, work and philosophy, edited by S. N. Sen was published on the occasion. (The photograph of Professor Saha facing page 217 was taken in his 60th year.)

During the last years of his life Saha was keeping an indifferent health. He was suffering from high blood pressure. But the end came rather suddenly. He passed away on 16 February 1956.

The life of Saha was in a sense an integral part of the growth of scientific research and progress in India, and the effect of his views and powerful personality would be felt for a long time to come in almost every aspect of scientific activity in the country. His dedication to science, his forthrightness and utter disregard of personal comforts in the pursuit of his chosen vocation will long remain an inspiration and an example.

Saha was married in June 1918 to Shrimati Radha Rani Saha. Her kindliness and genuine simplicity of character have won for her the affection and respect of generations of students and colleagues of Saha. Saha is survived by his wife, three sons and three daughters. The eldest son, A. K. Saha, is Professor in the Institute of Nuclear Physics.

In the preparation of this memoir I have drawn rather freely on the Commemoration Volume presented to Saha on his 60th birthday.

D. S. KOTHARI

Biographical Memoirs :: MEGHNAD SAHA

BIBLIOGRAPHY

1917. On Maxwell's stresses. Phil. Mag. 33, 256.
1917. The limit of interference in the Fabry-Perot interferometer. Phys. Rev. 10,782.
1918, On a new theorem in elasticity. J. Asiatic Soc. Bengal, New Series 14, 421.
1918. (With S. CHAKRAVARTI) On the pressure of light. J. Asiatic Soc. Bengal, New Series 14, 425.
1918. On the dynamics of the electron. Phil. Mag. 36, 76.
1918. (With S. N. BOSE.) On the influence of the finite volume of molecules on the new equation of state. Phil. Mag. 36, 199.
1919. Relativity dynamics of the electron. Phys. Rev. 13, 34.
1919. Radiation pressure. Astrophys. J. 50,220.
1919. Relativity law of elcctrical action. Phil. Mag. 37, 347.
1920. On selcctive radiation pressure and problems of the solar atmosphere. J. Dept Sci. Calcutta Univ. 2 (Physics), 51.
1920. Secondary spectrum of hydrogen. Phil. Mag. 40, 159.
1920. Ionization in the solar chromosphere. Phil. Mag. 40, 472.
1920. Elements in the sun. Phil. Mag. 40, 472, 809.
1920. Problcm of nova aquila III. J. Ind. Astr. Soc. (now defunct), 10, 36.
1921. Ionization in stellar atmosphere. Nature, Lond. 108, 131.
1921. Temperature radiation of gases. Phil. Mag. 41, 267.
1921. On electron-chemistry and its application to problems of radiation and astrophysics. J. Asiatic Soc. Bengal, 3 (Physics), 17.
1921. A physical theory of stellar spectra. Proc. Roy. Soc. A, 99, 135.
1921. Rubidium in the sun. Nature, Lond. 108,291.
1921. Versuch einer Theorie der Physikalischen Erscheinungen bei hohen Temperaturen, etc. Z. f. Physik. 6,40.
1921. The stationary H and K lines of calcium in stellar atmospheres. Nature, Lond. 107,488.
1921. The atomic radius and ionization potential. Nature, Lond. 107, 682.
1922. (With P. GUNTHER) Ionization of gases by heat. J. Dept Sci. Calcutta Univ.4 (Physics), 1.
1922. Temperature ionization of elements of the higher groups. Phil. Mag. 44, 1128.
1923. On the physical properties of elements at high temperatures. Phil. Mag. 46, 534.
1923. On continuous radiation from the sun. Nature, Lond. 112, 282.
1924. (With N. K. SUR) Thermal ionization. J. Ind. Chem. Soc. 1 9.
1924. (With N. K. SUR) On an active modification of nitrogen. Phil. Mag. 48, 421.
1924. The pressure in stellar reversing layer of stars and origin of solar continuous radiation. Nature, Lond. 114, 155.
1925. Ionization of stellar atmospheres and the steric factor. Mon. Not. R. Astr. Soc. 85, 977.
1925. Influence of radiation on ionization equilibrium. Nature, Lond. 115, 377.
1925. The phase rule and its application to problems of luminescence and ionization of gases. J. Ind. Chem. Soc. 2,49.
1925. The spectrum of Si+ (once ionized silicon). Nature, Lond. 116, 644.
1926. (With R. K. SUR) On the absolute value of entropy. Phil. Mag. 1, 279.
1926. (With R. K. SUR) Entropy of radiation. Phil. Mag. 1, 890.
1926. (With R. K. SUR) On the influence of radiation on ionization equilibrium. Phil. Mag. 1, 1025.

Biographical Memoirs :: MEGHNAD SAHA

1926. On the explanation of complicated spectra of elements. Volta Centenary Volume.
1926. Nitrogen in the sun. Nature, Lond. 117, 268.
1926. Application of subatomic thermodynamics to astrophysics. Nature, Lond. 117, 672.
1926. (With N. K. SUR and K. MAJUMDER) Uber einen cxperimentellen Nachweis der thermischen Ioniseirung der Elemente. Z. f. Physik, 40, 648.
1927. (With B. B. RAY) Uber das Mainsmith-Stonersche Schema des Aufbaus der Atome. Phys. Z. 28, 221.
1927. Uber ein neues Schema fur den Automaufbau. Phys. Z. 28, 469.
1927. On the detailed explanation of spectra of metals of the second group. Phil. Mag. 3, 1265.
1927. (With P. K. KICHLU) On the explanation of spectra of metals of group II. Phil. Mag. 4, 193.
1927. A note on the spectrum of neon. Phil. Mag. 4, 223, 231.
1928. (With P. K. KICHLU) Extension of the irregular Double Law. Ind. J. Phys. 2, 319; Nature, Lond. 121, 244.
1928. The origin of the spectrum of the solar corona. Nature, Lond. 121, 671.
1928. The origin of the nebulium spectrum. Nature, Lond. 121, 418.
1928. (With D. S. KOTHARI and G. R. TOSHNIWAL) Negatively modified scattering. Nature, Lond. 122, 398.
1928. (With K. MAJUMDER.) On the method of horizontal comparison in the location of spectra of elements. Ind. J. Phys. 3, 67.
1930. (With R. C. MAJUMDER.) On new methods in statistical mcchanics. Phil. Mag. 9, 584.
1930. Colours of inorganic salts. Nature, Lond. 125, 163.
1931. (With A. C. BANERJEE) Uber die Verteilung der Intensitat unter die Feinstruktur componenten der Serienlinien des Wasserstoffs und des ionisierten nach der Diracschen Theorie. Z. Physik. 68, 704.
1931. (With Y. BHARGAVA) The spin of the photon. Nature, Lond. 128, 870.
1931. (With R. K. SHARMA) Interpretation of X-ray term values. Bull. Acad. Sci. U.P. 1, 119.
1931. (With S. C. DEB) Colours of inorganic salts. Bull Acad. Sci. U.P. 1, 1.
1931. (With A. K. DUTTA.) Absorption spectra of saturated chlorides of multivalent elements. Bull. Acad. Sci. U.P. 1, 19.
1931. Spectroscopy in the service of chemistry. Sir P. C. Ray Seventieth Birthday Commemoration Volume of the Indian Chemical Society.
1932. (With S. BHARGAVA and J. B. MUKERJIE) Complex X-ray characteristic spectra. Nature, Lond. 129, 435.
1933. (With D. S. KOTHARI) A suggested explanation of ß-ray activity. Nature, Lond. 132, 747.
1934. (With D. S. KOTHARI) On the ß-ray activity of radioactive bodies. Proc. Acad. Sci. India, 3, 257.
1934. (WithJ. B. MUKERJIE) Inner conversion in X-ray spectra. Nature, Lond. 133, 377.
1934. The upper atmosphere. Proc. Nat. Inst. Sci. India, 1,217-241.
1936. The origin of mass in neutrons and protons. Ind. J. Phys. 10, 141.
1936. (With L. S. MATHUR) Active nitrogen. Proc. Nat. Acad. Sci. India, 6, 120.
1936. Can electrons enter the nucleus? Sci. & Cul. 2, 273.
1936. (With AMARNATH TANDON) A new model demountable vacuum furnace. Proc. Nat. Acad. Sci. India, 6, 212.
1937. Stratosphere solar observatory. Harvard Coll. Obs. Bull. No. 905, 1.

Biographical Memoirs :: MEGHNAD SAHA

1937. Action of ultra-violet sunlight on the upper atmosphere. Proc. Roy. Soc. A, 160, 55.
1937. Molecules in interstellar space? Nature, Lond. 139, 840
1938. (With R. N. RAI and K. B. MATHUR) On the propagation of electromagnetic waves through the earth's atmosphere. Proc. Mat. Inst. Sci. India, 4, 1,53.
1938. (With R. N. RAI) On the ionisation of the upper atmosphere. Proc. Nat. Inst. Sci. India, 4, 3, 319.
1939. (With K. B. MATHUR.) Propagation and total reflection of electromagnetic waves in in the ionosphere. Ind. J. Phys. 13, 1.
1940. (With S. C. SIRKAR and K. C. MUKHERJI) Structure of atomic nuclei. Proc.Nat. Inst. Sci. India, 6, 1,45.
1942. On a physical theory of the solar corona. Proc. Nat. Inst. Sci. India, 8, 1, 99.
1945. A physical Theory of the solar corona. Proc. Phys. Soc. 57, 271.
1945. (With D. BASU) Capture of electrons by positive ions while passing through gases. Ind. J. Phys. 19, 121.
1945. (With B. K. BANERJEE) Wave-treatment of the propagation of electromagnetic waves in the ionosphere. Ind. J. Phys. 19, 159.
1946. (With A. K. SAHA) On nuclear energetics and ß-activity. Trans. Nat. Inst. Sci. India, 2,7, 193.
1946. (With A. K. SAHA.) Nuclear energetics and ß-activity. Nature, Lond. 158, 6.
1946. Conditions of escape of radio-frequency energy from the sun and stars. Nature, Lond. 158, 549.
1946. Origin of radio-waves from the sun and the stars. Nature, Lond. 158, 717.
1947. (With B. D. NAG CHOWDHURY) Measurement of geological time in India - the age of rocks and minerals. Trans. Nat. Inst. Sci. India, 2, 8, 273.
1947. (With B. K. BANERJEE AND U. C. GUHA) On the propagation of E.M. waves through the upper atmosphere. Ind. J. Phys. 21, 181.
1947. (With B. K. BANERJEE AND U. C. GUHA) On the conditions of escape of micro-waves of radio-frequency range from the sun. Ind. J. Phys. 21, 199.
1949. Note on Dirac's theory of magnetic poles. Phys. Rev. 75, 1968.
1951. (With B. K. BANERJEE AND U. C. GUHA) Vertical propagation of electromagnetic waves in the ionosphere. Proc. Nat. Inst. Sci. India, 17, 205.
1951. Occurrence of stripped nuclei of neon in primary cosmic rays. Nature, Lond. 167,476.
1954. Determination of the electron concentration and the collision frequency in the ionospheric layers from polarization patterns of the 0 and X waves. Proc. Mixed Commission on the Ionosphere, Brussels. 211.
1956. Fuel in India. Nature, Lond. 177, 923.

Biographical Memoirs :: MEGHNAD SAHA

ARTICLES PUBLISHED IN Science and Culture (Calutta)

The abbreviation `Ed. Art.' stands for signed editorial article; `unsigned' stands for unsigned editorial note. The bibliography, up to 1953, is reproduced from Professor Meghnad Saha, his life, work and philosophy (1954).

Vol. I (1935-36)

Science & culture (Ed. Art.), p. I.
Ultimate constituents of matter, p. 12.
The great Quetta earthquake (Ed. Art.), p. 63.
The march towards absolute zero. p. 132.
A common script for India. (Ed. Art.), p. 117.
The Carnegie Educational Trusts (Ed. Art.), p. 215.
Electricity - its use for the public and for industries (Ed. Art.), p. 303.
The Carnegie Institution of Washington (unsigned), p. 330.
The fiftieth birthday of Niels Bohr (unsigned), p. 337.
Public supply of electricity in India (Ed. Art.), p. 367.
Sir U. N. Brahmachari (unsigned), p. 407.
Archaeological excavations in India (Ed. Art.), p. 439.
The Indian Institute of Sciences, Bangalore (Ed. Art.), p. 523.

Vol. II (1936-37)

(With P. L. KAPUR) Conference on Nuclear Physics, p. 133.
Irrigation research in India (Ed. Art.), p. 281.
Industries and scientific research (Ed. Art.), p. 413.
Problems of industrial development in India (Ed. Art.), p. 529.

Vol. III (1937-38)

On the national supply of electricity (Ed. Art.), p. 65.
Indian national reconstruction and the Soviet example (Ed. Art.), p. 185.
(With D. S. KOTHARI) Obituary of Lord Rutherford of Nelson, p. 300.
Indian Science Congress Association, 1914-38 (Ed. Art.), p. 307.
Need for a power research and investigation board in India (Ed. Art.), p. 405.
Minor plants (unsigned), p. 312.
(Wilh A. N. TANDON) The intelligent man's guide to the production and economics of electrical power, pp. 506, 574.
Symposium on India's power supply (unsigned), p. 594.
Fight of Oxford municipality against Lord Meston and others (unsigned), p. 602.

Vol. IV (1938-39)

The next 25 years of science in India (Ed. Art.), p. I.
Records of the Royal Society of London (unsigned), p. 91.
Review of the Rockefeller Foundation for 1937 (unsigned), p. 99,
Congress President on national reconstruction (Ed. Art.), p. 137.
Technical assistance to Indian industry by the Govt. of India (unsigned), p. 147.
Symposium on Weather prediction (unsigned), p. 160.
On a national scheme of education (Ed. Art.), p. 199.
Industrial India (Ed. Art.), p. 36. 5.
The age of Mahabharata (unsigned), p. 182.
Solar control of the atmosphere, p. 545.
Need of calendar reform (Ed. Art.), p. 601.
The reformed calendars and the Gregorian calendar, p. 603.
National planning in Sweden (Ed. Art.), p. 669.

Biographical Memoirs :: MEGHNAD SAHA

Vol. V (1939-40)

The Indus Valley 5000 years ago (unsigned), pp. 6, 89.
Centenary of decipherment of the Brahmi and Kharosthi alphabets (unsigned), p. 148.
James Princep (unsigned), p. 153.
The War comes (Ed. Art.), p. 265.
Work of the Archaeological Survey of India (Ed. Art.), pp. 377, 451.
The four-fold ruin of India (Ed. Art.), p. 499. ,
National Research Council for India (Ed. Art.), p. 571.
Scientific research in national planning (Ed. Art.), p. 639.

Vol. VI (1940-41)

Wanted a national fuel policy (Ed. Art.), p. 61.
(With P. K. SEN CHAUDHURY) Physics in aid of medicine, p. 110.
On the use of science and scientists (Ed. Art.), p. 1m.
Right thinking (Ed. Art.), p. 311.
Science in War (Ed. Art.), p. 489.
Need for a school of glass technology in India (Ed. Art.), p. 555.
Sir Shah Md. Suleiman, p. 644.
Uranium fusion, p. 694.

Vol. VII (1941-42)

Science teaching in schools (Ed. Art.), p. 61.
Rabindra Nath Tagore (unsigned), p. 123.
A common language for India (Ed. Art.), p. 173.
The mystery of the solar corona solved, p. 247.
Sir M. Visvesvaraya (unsigned), p. 274.
Automobile industry in India (Ed. Art.), p. 465.
The late Prof. W. Nernst, p. 518.
The late Sir William Henry Bragg (unsigned), p. 544.

Vol. VIII (1942-43)

Civilizations in transition (unsigned), p. 2.
The late Rai Bahadur R. P. Chanda (unsigned), p. 65.
Science and war effort in Great Britain and India (Ed. Art.), p. 95.
Twenty-five years of the Soviet Union (Ed. Art.), p. 145.
(With S. N. SEN) Oil and invisible imperialism, p. 150.
The renaissance of China (Ed. Art.), p. 195.
Technological revolution in industry -- how the Russians did it (unsigned), p. 398.
Industrial research and Indian industries (Ed. Art.), p, 465.
Gauripati Chatterjee (unsigned), p. 163.

Biographical Memoirs :: MEGHNAD SAHA

Vol. IX (1943-44)

Proposal for reform of the Govt. Organization for Scientific and Industrial Research (Ed. Art.), p. 1.
University College of Science, Calcutta (unsigned), p. 19.
Flood (Ed. Art.), p. 95.
Shakespeare on astrology (unsigned), p. 142.
Basic principles of organizations of scientific rcsearch (Ed. Art.), p. 173.
Prof. Hill on the organization of scientific research (unsigned), p. 308.
Post war educational development in India (Ed. Art.), p. 405.
(With K. Ray) Training of the Tennessee River, p. 418.
Famines, Royal Commissions and Commercial Commissions (Ed. Art.), p. 509.

Vol. X (1944-45)

Department of planning and development (Ed. Art.), p. 7.
(With K. RAY) Planning for the Damodar Valley, p. 20.
India's need for power development (Ed. Art.), p. 61.
Principles of regional planning (Ed. Art.), p. 17i.
Some constitutional hindrances to development of India's natural resources (Ed. Art.), p. 455

Vol. XI (1945-46)

Development of resources and Indian constitution (Ed. Art.), p. I.
The 220th Anniversary of the U.S.S.R. Academy of Sciences (Ed. Art.), p. 49.
(With S. N. SEN) Institutions under the U.S.S.R. Academy of Sciences, p. 55.
(With B. D. NAG CHAWDHURY) The story of the atomic bomb, p. 111.
Industrial research (unsigned), p. 119.
The logic of the atom bomb (unsigned), p. 212.
Britain's part in the evolution of atom bomb (unsigned), p. 214.
Planning or muddling (Ed. Art.), p. 215.
Royal Asiatic Society of Bengal (Ed. Art.), p. 451.
Obituary of Sir U. N. Brahmachari (unsigned), p. 447.
The Damodar Valley Reclamation Scheme (unsigned), p. 513.
The atom bomb, p. 645.

Vol. XII (1946-47)

Our national crisis (Ed. Art.), p. 253.
Patterns of planning in different countries (Ed. Art.), p. 297.
Association of Scientific Workers (India), p. 323.

Vol. XIII (1947-48)

Multi-purpose development of Indian rivers (Ed. Art.), p. 3.
National Research Council (Ed. Art.), p. 123.
Industrial utilization of atomic power in India (unsigned), pp. 86, 134.
Release of atomic energy (Ed. Art.), p. 167.
Problems of independent India (Ed. Art.), pp. 358, 471.

Vol. XIV (1948-49)

Department of Scientific Research, I and 2 (Ed. Art.), p. 41.
University Grants Committee (Ed. Art.), p. 215.

Biographical Memoirs :: MEGHNAD SAHA

Vol. XVI (1950-51)

National Planning Commission (Ed. Art.), p. 2.

Vol. XVII (1951-52)

Five year plan (Ed. Art.), p. 51

Vol. XVIII (1952-53)

Education in India (Ed. Art.), pp. 1, 53.
Reform of the Indian calendar, pp. 57,109.
Need for a central geophysical institute (Ed. Art.), pp. 103, 355.
Rethinking our future (Ed. Art.), pp. 399, 449, 557.
The industrial policy of the Planning Commission, p. 452.

Vol. XIX (1953-54)

Technical autonomy in industrialization (Ed. Art.), p. 471.
(With B.D.N.) The thermonuclcar weapon, p. 575.

Vol. XX (1954-55)

The solar eclipse of June 30, 1954, p. 2.
Obituary: Sir Lewis L. Fermor, p. 28.
The World Calendar Plan, p. 108.
Atomic energy in India (Ed. Art.), p. 205.
Future of atomic energy in India, p. 208.
The University Grants Commission Bill, 1954 (Ed. Art.), p. 409.
Draft Second Five-year Plan (Ed. Art.), p. 575.
Technological evolution -- the basis for economic freedom, p. 578.

Vol. XXI (1955-56)

Atomic weapons, disarmaments and peaceful uses of atomic energy, p. 66.
Thc Report of the Disarmaments and Atomic Weapons Commission of the World Peace Assembly -- Helsinki, p. 70.
The Atomic Energy Conference at Moscow, p. 76.
End of an unscientific era (Ed. Art.), p. 117.
(With A. P. PATRA AND S. K. SEN) Observers' notes on physics and reactor sessions of Geneva Conference, p. 129.
List of papers presented at the Geneva Conference, p. 113.
Ninth Session of the International Astronomical Union. Dublin - Ireland, p. 183.
Reports of the States Reorganization Commission, p. 223.
(With A. BOSE AND D. BASU) The Nobel Prize Awards in Physics, 1955, p. 363.
(With MANUJENDRA LAL CHAUDHURI.) The Nobel Prize Award in Physics, 1955 (II), p. 513.
Institute of Nuclear Physics, p. 586.

Biographical Memoirs :: MEGHNAD SAHA

MISCELLANEOUS PAPERS

n.d. Need for a hydraulic research laboratory in Bengal. Sir P. C. Ray Commemoration Volume published on the occasion of his 60th birthday. Calcutta.
1937. The mission of the physicist in national life. Ind. J. Phys. 11,5.
1938. The problem of Indian rivers. Proc. Nat. Inst. Sci. India, 4, 1.
1945. Science in social and international planning, with special reference to India. Nature, Lond. 155, 221.
1948. Scientific research in India. Proc. Nat. Inst. Sci. India, 11, 4. 161.
1952. Suggested reform of the Indian calendar. Nature, Lond. 169,961.
1953. Different methods of date recording in ancient and medieval India, and the origin of the Saka era. J. Asiatic Soc. Bengal, 19, 1.

BOOKS

1919 (With S. N. BOSE) The principle of relativity (English translation of Einstein's papers). Calcutta University.
1931. (With B. N. SRIVASTAVA.) A textbook of heat (including kinetic theory of matter, thermodynamics, statistical mechanics and theories of thermal ionization). Allahabad: Indian Press, pp. xxv + 771 (Fourth edition published in 1958).

ON PROFESSOR SAHA AND HIS WORK

1954. Professor Meghnad Saha -- His life, work and philosophy; ed. by S. N. Sen, Indian Association for the Cultivation of Science -- Meghnad Saha 60th Birthday Committee, pp. 175.
1954. Meghnad Saha. Sci. & Cul. 19, 442.
1956. Meghnad Saha Number. Sci. & Cul. 22, No. 4, October 1956.
1956. Obituary: Professor Meghnad Saha, F.R.S., by F. J. M. Stratton. Nature, Lond. 177, 917.