Meghnad Saha

Meghnad Saha মেঘনাদ সাহা
Meghnad Saha in Berlin
Born	6 October 1893(1893-10-06) Shaoratoli, Dhaka, Bengal, British India
Died	16 February 1956(1956-02-16) (aged 62)
Residence	India
Nationality	Indian
Fields	Physics
Institutions	Allahabad University University of Calcutta Imperial College London
Alma mater	Dhaka College Presidency College of the University of Calcutta
Known for	Thermal ionisation

Meghnad Saha FRS^[1] (Bengali: মেঘনাদ সাহা) (6 October 1893 – 16 February 1956) was an Indian astrophysicist best known for his development of the Saha equation, used to describe chemical and physical conditions in stars.

Early life

Meghnad Saha was born in a small village named Seoratali, about 40 km from Dhaka (in present Bangladesh). The youngest of the five sons of Jagannath Saha and Bhubaneswari Debi, Meghnad belonged to a poor family and struggled to rise in life. His father was reluctant to allow him to undergo higher education; he wanted him to assist him in shopkeeping. With some persuasion from his eldest son Jayant and Meghnad's primary school teachers, he relented, and Meghnad went to the neighbouring village to live there and attend an English-medium school. Here he was lucky in that one Mr. Ananta Kumar Das, a medical practitioner, took interest in Meghnad and offered him free boarding and lodging. In 1905, he joined the Dhaka Collegiate School. Here he not only received a free studentship, but also a stipend. However he lost both his free studentship and stipend when he participated in a boycott against the then British Governor of Bengal Sir Bampfylde Fuller when he came on a visit to Dacca. He managed to pull through by joining the Kishorilal Jubilee School where he again received a free studentship and a stipend. Around this time Saha joined the Bible classes run by the Dacca Baptist Society. In a test that was conducted, Saha stood first and won a handsome prize of Rs.100/- plus a beautifully bound copy of the Bible. In 1909 Saha passed the Collegiate entrance exam, standing first among the students from East Bengal, with highest marks in Mathematics, English, Sanskrit and Bengali. This got him entry into the Intermediate Dhaka College, where he spent two years studying Intermediate. During this time he also took private lessons in German which later was to stand him in good stead.
In 1911 he ranked third in the ISC exam. In the same year Saha came to Calcutta and joined the Presidency College to study for the B.Sc. degree in Applied Mathematics. Presidency College by then had spawned numerous luminaries, and Saha found himself surrounded by many: Satyendra Nath Bose, Jnan Ghosh, N.R. Sen, and J. N. Mukherjee were his classmates, P.C. Mahalanobis was one year his senior, N. R. Dhar was senior by two years, while Netaji Subhash Chandra Bose was one year his junior. His teachers included Jagadish Chandra Bose in physics, Prafulla Chandra Roy in chemistry, D.N. Mallik and C. E. Cullis in mathematics.^[2] After B.Sc. came M.Sc. and once again S.N. Bose was his classmate. In M.Sc. and B.Sc. Saha secured the second rank, while Bose stood first, while in the M.sc. exam both stood first, Bose in Pure Mathematics and Saha in Applied Mathematics.^[3]
While in college during 1913 through 1915, Meghnad got involved with Anushilan Samiti to take part in freedom fighting movement. Bagha Jatin, a famous freedom fighter, was used to visit his hostel for building student organization., Saha flirted a bit with the idea of joining hands with revolutionaries in their fight against the British. However he soon gave up on the idea, his goal was to get a job, earn money and support his family. After college he tried to enter the Indian Finance Service, but he was denied permission to appear in the exam as he was suspected of having contacts with revolutionaries; besides, there was also the boycott he had participated in as a school student. In order to procure some income, he started giving private tutions. It was around this time that Sir Ashutosh Mukherjee became the Vice Chancellor of Calcutta University, and he opened a new College of Science for post-graduate studies and research - this was made possible because of the magnificent donations of two eminent lawyers of Calcutta, Tarak Nath Palit and Rash Behari Ghose.^[2] He offered lecturerships to both Saha and Bose in the Department of Mathematics in this college but because they could not get along with Dr. Ganesh Prasad, the professor, he transferred them to the Physics Department where C.V. Raman had been appointed the Palit Professor. In later life he was close to Amiya Charan Banerjee, a renowned mathematician at Allahabad University.

Scientific career

Selective Radiation Pressure

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^[4][5] and quickly followed it up with several more in the next couple of years. This was followed by papers on the dynamics of the electron. He derived, on the basis of the Special theory of Relativity, the Liénard–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.^[5] These were substantial enough for the Calcutta University to award him the D.Sc. degree in 1918. In between, Saha got married to Radharani (he had believed that a celibate life was most fit for him until he read The Cloister and the Hearth, which resolved him to marry). At this point of time he became interested in the phenomenon of selective radiation pressure. The question that piqued his curiosity was that how come a heavier element like Calcium is present up to a greater height compared to a lighter element like Hydrogen, apparently defying gravity. 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. Several models had already been proposed to explain this anomaly, all of them banking on the possibility of a sharp decrease of density with increase in height that might negate the effect of increased weight of the element. One such model suggested by Schwarzschild predicted that at a height of around 3500 km, there would be only one atom in a billion cubic metres. However the flash spectra showed that the abundance of atoms at great heights was much higher, clearly debunking such speculations. Saha gave this matter a great deal of thought and concluded that "It seems to be the general opinion of the astrophysicists that there is some sort of a repulsive force on the Sun which neutralizes the greater part of gravity. " In a short paper entitled On Radiation-Pressure and the Quantum Theory"^[6] contributed in 1919 to the Astrophysical Journal, Saha showed that what countered gravity was selective radiation pressure.^[7]
The idea of Radiation Pressure was by itself not new. It was a natural consequence of Maxwell's Electromagnetic theory of light, and laboratory experiments had already been performed to demonstrate the existence of radiation pressure. However Maxwell's theory also predicted that when the size of the object is reduced, the pressure decreases, becoming vanishingly small when the size of the particle dwindles to that of an atom. Saha's theory seemed to contradict this because it claimed that radiation lifts the atoms up into the chromosphere in defiance of solar gravity. Saha explained this apparent difference: "An explanation of the existence of radiation-pressure on molecules is furnished when we apply the quantum theory in place of the old continuous theory of light."
According to him, following Einstein and Planck, one visualizes light energy to be composed of ‘localized in packets of energy hν’. Now supposing that one such pulse is absorbed by an atom of mass M. The light pulse comes with a momentum (hν/c), and when it is absorbed this momentum is transferred into the atom, which then moves with a velocity v = (hν/cM). However when actual values were substituted, the velocity came out to be rather small. Saha countered: "It should be remembered that v is really an impulsive velocity and is one of the nature of an acceleration. The total velocity acquired by a Hydrogen atom per second will depend upon the number of kicks of light it experiences per second, and provided this is sufficiently great the velocity acquired may rise to enormous values. " Thanks to such velocities, atoms could be carried away to long distances from the chromosphere, creating a blanket of atoms thicker than what the theory of Schwarzschild and its concomitants predicted. However as the atom will not absorb a light pulse of any arbitrary frequency ν but only a frequency that corresponds to one of the allowed transitions, in this respect the atom is choosy, and therefore selective. Other factors which govern the value of the pressure are:

1. How many photons there are at frequency ν in the spectrum coming out of the photosphere.
2. What sort of absorption frequencies are available to the atom.
3. How intense is the Blackbody spectrum at those frequencies.

In this way we can understand why Calcium is present at higher levels than hydrogen, it is because the radiation pressure on the former is more than on the latter. He described his findings in a paper entitled The Stationary H- and K-lines of Calcium in Stellar Atmosphere which he submitted to the Nature magazine in 1921."^[8]

The Chromosphere Puzzle

By 1915, the subject of Stellar Spectroscopy had garnered substantial attention so that many scientists were devoting their efforts to discern its mysteries. The foundations of the subject were laid by Fraunhofer and Kirchhoff. The next important landmarks was the work of Higgins and Miller who reported on the Fraunhofer spectra of about fifty of the brightest stars. They concluded that all the stars they had examined had a chemical composition similar to the Sun. By 1920, over two hundred thousand stars had been studied and classified. This spawned a general consensus that if one understood what was going on in the sun, one could figure out what was going in the stars as well. But in spite of the welter of information regarding it, the Sun remained an enigma. Lockyer had said that lines (in the flash spectrum) originating at the top of the chromosphere were similar to those seen in spark spectra. He also said that the spark lines were enhanced, the enhancement being due to a stimulus, which he held, was temperature. However this theory had its detractors. It was conceivable that the enhancement came not only from high temperature, but some other agency was providing the stimulus as well. Saha later recalled:

I was a regular reader of German journals which had which had just started coming after four years of First World War, and in the course of these studies I came across a paper by J.Eggert....in which he applied Third Law of Thermodynamics to explain high ionisation in stars due to high temperatures, postulated by Arthur Stanley Eddington in the course of his studies on stellar structures....While reading Eggert's paper I saw at once the importance of introducing the value of the ionisation potential in the formula of Eggert, for calculating accurately the ionisation, single or multiple, of any particular element under any combination of temperature and pressure. I thus arrived at a formula which now goes by my name. Owing to my previous acquaintance with chromospheric and stellar problems, I could at once see its application...

European sojourn and Thermal Ionisation

Saha now realized that in order to delve deeply into the matter, he should go to Europe and consult with other eminent astrophysicists to aid him in his research. He got hold of two books on astronomy by Agnes Clerke, which furthered his interest in the subject. But he was short of money, so he had to compete for studentships and fellowships. Among other things, the competition required him to submit a technical essay and he wrote one entitled On the Harvard Classification of Stellar Spectra. Saha's essay was so much superior to the other entries that both the Premchand Roychand Studentship and the Guru Prasanna Ghosh Fellowship easily came to him.^[9] With some guarantee for money in pocket, he set sail for Europe in September 1919. After reaching London Saha realized that he was short of money of again, and something had to be done quickly both on the financial side and the scientific as well. Fortunately he ran into an ex-classmate who was then at the Imperial College. He acquainted Saha with Prof.A.Fowler, who himself was a famous stellar astrophysicist and a former assistant to Lockyer. Fowler was impressed by his prize-winning essay and permitted him to work in his lab under his guidance. Under his guidance, Saha rewrote the essay, giving it a new title: On a Physical Theory of Stellar Spectra.^[4][10] Fowler communicated this paper to the Royal Society, which promptly published it in its proceedings; the paper attracted wide attention in America. This thesis won him the Griffith Prize of the Calcutta University in 1920."^[11] Saha later reminisced:

I took about four months in rewriting the 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 whenever I went a little astray out of mere enthusiasm.

Commenting on the relationship, astronomer 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." In addition to this paper he also published three other papers on his astrophysical research in the first six months of 1920 in the Philosophical Magazine viz. Ionisation of the Solar Chromosphere (March 4, 1920),^[4] On Elements in the Sun (22 May 1920)^[4] and On the Problems of Temperature-Radiation of Gases (25 May 1920).^[4] In these papers Saha laid the foundation of what later came to be known as the Theory of Thermal Ionisation. The absorption lines of stellar spectra differ widely, with some stars showing virtually nothing but hydrogen and helium lines while others show vast numbers of lines of different metals. Saha's great insight was to see that all these spectral lines could be represented as the result of ionization. He saw that the degree of ionization, i.e., the number of electrons stripped away from the nucleus, would depend primarily on temperature. As the temperature increases, so does the proportion of ionized atoms. The remaining neutral atoms will thus produce only weak absorption lines that, when the temperature gets high enough, will disappear entirely. But the singly, doubly, and even triply ionized atoms will absorb at different sets of wavelengths, and different sets of lines will appear in stellar spectra, becoming stronger as the proportions of these ions grow.^[12] He also formulated what is known as the Saha equation. This equation is one of the basic tools for interpretation of the spectra of stars in astrophysics. By studying the spectra of various stars, one can find their temperature and from that, using Saha's equation, determine the ionisation state of the various elements making up the star.Besides continuing on his works in astrophysics, Saha was also keen to pursue experiments to verify his theory of thermal ionisation, which however called for advanced laboratories equipped with high-temperature facilities. Since such labs were not available in England, on Fowler's advice, Saha wrote to Nernst, who promptly extended him an invitation to visit his lab and perform his experiments. Saha spent about a year in Nernst's lab and this proved an immense boon. Right next to the lab was held every week the University Colloquium, and he attended all of them. This enabled him to meet many eminent German physicists like Max Planck, Max von Laue and Einstein. Meanwhile Saha sent a copy of his paper on his stellar spectra to Sommerfeld who immediately invited him to Munich to deliver a seminar. This was done in May and the lecture was published in the Zeitschrift fur Physik Vol 6.^[9] This visit coincided with that of Rabindranath Tagore, whom Saha did not know at that time. Sommerfeld acquainted them; Tagore received him very affectionately, enquired about his work, and invited him to visit Santiniketan on his return to India.
From Germany Saha went to Switzerland and then back to England, where he met Eddington at Cambridge. Eddington invited him to his house, and there he was introduced to Milne, who was then Eddington's assistant. Milne told Saha that he had seen his paper on radiation pressure in Nature and that he had done further work on the subject. Milne also added that he was collaborating with R.H.Fowler on extending Saha's work. (In fact this theory has seen come to be known as Milne's theory of selective radiation pressure.) Saha later lamented: "I might claim to be the originator of the theory of Selective Radiation Pressure...Milne read a note of mine in nature and in his paper he mentioned my contribution in a footnote, though nobody appears to have noticed it."

Stellar Spectroscopy

Before leaving for Germany, Prof. H.H.Turner of Oxford suggested that the Mount Wilson Observatory in America will be the best place for his kind of work and advised him to write to George Ellery Hale, Director of the Mount Wilson Observatory. On 9 July 1921, Saha wrote to Hale: "I shall be very glad if someone at the Mount Wilson Solar Observatory undertakes the work suggested overleaf. My means are too limited and my university is poorly provided for astrophysical work, I see no prospects of ever being able to carry out the ideas contained in my papers. It will be a source of great pleasure for me to find that my exertions have resulted in throwing some light on some dark problems in astrophysics."^[4] In the enclosure he added his predictions made in his four papers published in the philosophical Magazine the previous year. There was no reply. However around this time Henry Norris Russell of Princeton University took quick and serious notice of Saha's work. He convinced Hale of the authenticity of Saha's work, and under their coordination, the general attack on spectra began in Mount Wilson Observatory. Saha however was not asked to join them. Hence he was resigned to wok with limited data and scientific instruments, which however did not deter him in the least. Meanwhile the Harvard College Observatory had accumulated mountains of data and Russell was concerned as to what it all meant. Between 1908 and 1913 he applied his mind vigorously to the problem and came to the conclusion that the data could be comprehensively represented as a map. Such a plot was independently developed by Hertzsprung and so it is often called Hertzsprung–Russell diagram. However, while making the plot, he found that most stars clustered in a band. This could not be the case unless the alphabets were in some mysterious way related to some physical parameter of the star. Pickering and Cannon proposed the Harvard Classification Scheme, because they observed that the spectra changed continuously across the sequence. But none was sure as to what caused this change. Russell suspected that it was the temperature of the stellar atmosphere that caused the change; he however could not explain how temperature variation caused a gradual change in the absorption spectra.
Russell, however, was not aware that Saha had already taken the first step in this direction in his prize-winning essay (under A.Fowler's guidance). Saha began that article by quoting Russell as follows: "The spectra of stars show remarkably few radical differences in type. More than 99% of them fall into one or the other of the six great groups which during the classic work of the Harvard College Observatory...received designations...by the rather arbitrary letters B A F G K M. That there should be so few types is noteworthy, but much more remarkable is the fact that they form a continuous series... Russell is of the opinion that the principal differences in the stellar spectra arise in the main from variations in single physical variable in the stellar atmosphere...". In his paper Saha showed that

1. His analysis substantiated Russell's views that continuous variation of stellar spectra among the various types was due to the variation of a single parameter.
2. The parameter in question was temperature.
3. He could convert the arbitrary Harvard scale of alphabets into a temperature scale based on spectral information by the method of marginal displacement.

Although he was the one who originally conjured up the idea of converting the Harvard scale into a temperature scale, there were some practical difficulties, including in precisely determining when a line just disappears. Fowler and Milne extended the formula by fixing the temperature scale after observing when the line intensity became maximum. Hence this achievement is generally attributed to this duo. Cecilia Payne-Gaposchkin, who was then working in the Harvard College Observatory later recollected:

In my last year at Cambridge, I had come to know E.A.Miles, who with Ralph Fowler had just published the historic paper on stellar atmospheres. They in turn had been inspired by the brilliant idea with which Meghnad Saha had applied the principles of physical chemistry to the ionisation of stellar material, the idea that gave birth to modern astrophysics...

Back to India

In Allahabad

In November 1921 Saha returned to India and joined the Calcutta University as Khaira Professor of Physics, a new Chair created from the endowment of Kumar Guruprasad Singh of Khaira. However the university was going through acute financial crisis, made no better by the enmity of Lord Ronaldshay, the then Governor of Bengal, towards Sir Ashutosh Mukherjee, who was then serving his second term as the Vice Chancellor of the university. Saha was caught up in this turmoil and where he was concerned, he could not get an assistant, he could not buy equipment and he even had problems with lab space. Much as he loved Calcutta, he concluded that he couldn't possibly continue his research there, and decided to leave. Offers came from Aligarh Muslim University and Benaras Hindu University, but he rejected both in favour of the Allahabad University, chiefly because some of his friends were on the Executive Council of that university, who he hoped would assist him financially to conduct his researches. At Allahabad before he could start research work he had to improve the workshop, the laboratory and the library. Moreover, he found hardly any time for research after discharging heavy teaching responsibilities. But Saha was not to be distracted by adverse conditions. And very soon research papers started appearing from Saha and his students. Among his collaborators at Allahabad were N.K. Sur, P.K. Kichlu, D.S. Kothari, R.C. Majumdar, K.B.Atmaram Mathur and B.D. Nag Choudhary. In 1927 the Italian Government organised a grand International Conference to commemorate the birth centenary of Alessandro Volta. the venue was Como, and the principal organiser was Fermi. Saha got an invitation, and there he presented a paper on the analysis of complex spectra, that being then the topic of his interest. From Como, Saha proceeded to Oslo in Norway to join an expedition organised by Prof.L.Vegard of Oslo University to observe a forthcoming total solar eclipse. For this purpose, the party journeyed to Ringebu.
The same year he became a fellow of the Royal Society of London.^[1][13] He was also elected a life member of the Astronomical Society of France and was made a Foundation Fellow of the Institute of Physics in London.^[13] This chanced him an audience with the then Governor of United Provinces Sir William Sinclair Morris, and learning that he was once a classfellow of Ernest Rutherford, took the opportunity to tell him about the poor condition of the lab. The Governor was moved and immediately sanctioned a research grant of Rs. 5000/- per month. Realising that this was by no means enough, he wrote to Sir Tej Bahadur Sapru, imploring him to write to the Central Government in Delhi recommending a research grant. However his request fell to deaf ears, and so he turned to the Royal Society. Understanding his plight, the Society promptly granted a yearly sum of Rs. 1500/-, and now he could afford to concentrate fully on research work without monetary problems. In the next year 1932, he became the University Professor of Physics in the university.
Around this time Saha felt the necessity of developing a science academy to instill in the students the passion to pursue research and other innovative works. He was inspired in this idea by the successful heritage of similar academies like the Royal Society in England, the French Academy of Sciences in Paris, the Prussian Academy of Sciences in Berlin, the Russian Academy of Sciences in Moscow. The idea came to him when in 1930 the Indian Science Congress Association met in Allahabad under the presidentship of C. S. Christopher. Delivering an address on the occasion, the Governor Malcolm Hailey said that if a scientific body could motivate research in the university departments and steer it for public benefit, then it might become possible for the Government to offer grants for research. Saha took this hint and thanks to his effort the U.P. Academy of Sciences came into existence. Despite its name, National Academy of Sciences essentially functioned as a regional body. This prompted him to envision an organisation with an all-India character and thus in 1934 he proposed the founding of an Indian Academy of Sciences. On this issue there was strong difference of opinion between him and Raman and eventually Raman announced in Bangalore the founding of the Indian Academy of Sciences. This was unacceptable to Saha who continued his efforts and as a result there came into existence in 1935 the National Institute of Sciences, India with its headquarters in Calcutta. The formation was formally announced on January 7 in the Senate Hall of the Calcutta University under the Chairmanship of the J.H. Hutton. L.L. Fermor was elected the first president of the Institute. The same year he also founded the Indian Science News Association at Calcutta. Its main objective was to disseminate science amongst the public.The Association started publishing its journal called Science and Culture. On receiving, a copy of the first issue of the Journal, Netaji Subhash Chandra Bose was impressed and he wrote: "The appearance of Science and Culture is to be warmly welcomed not only by those, who are interested in abstract science but also by those who are concerned with nationbuilding in practice. Whatever might have been the views of our older "Nation builders" we younger folk approach the task of nation building in a thoroughly scientific spirit and we desire to be armed with all the knowledge which modern science and culture can afford us. It is not possible however, for political workers with their unending preoccupations to glean that knowledge themselves, it is therefore, for scientists and scientific investigators to come in their rescue." Saha himself wrote more than 200 articles in Science and Culture on a wide range of topics which included: organization of scientific and industrial research, atomic energy and its industrial use, river valley development projects, planning the national economy, educational reforms and modification of Indian calendar. The journal is presently running in its 76th volume. Later, on his initiative, the headquarters of the National Institute of Sciences was shifted to Delhi May 1946 and the name was changed to the Indian National Science Academy.^[14]
In 1936 Saha received a fellowship from the Carnegie Trust of the British Empire, and he went on an extended outing that took him to countries like Iraq, Syria, Jordan, Israel. At Munich he was happily reunited with Sommerfeld. He then proceeded to London to attend the centenary celebrations of the Physics society where Max Planck was the chief guest. From London Saha went to Oxford and spent a month in the company of Milne. Then he visited the Harvard College Observatory in Boston. here he met many noted scientists like Harlow Shapley, Donald Menzel, and Cecilia Payne-Gaposchkin. Moving west, he made a grand tour visiting many observatories and meeting famous people like Hubble, Walter Adams, and lastly Lawrence in Berkeley. Saha and Lawrence had earlier met in Copenhagen in 1927, but by now Lawrence was famous as the inventor of the cyclotron. This contact proved useful and later Lawrence helped Saha to some extent to construct a cyclotron in Calcutta. From there, he went to Chicago to visit the Yerkes Observatory. Returning to Harvard, he attended the centenary celebrations of the Harvard University. It was then he wrote a short note entitled A Stratosphere Solar Observatory,^[15] which was published in the Harvard College Observatory Bulletin, where he explicitly suggested the observation of the solar spectrum at a height greater than 40 km, for he reckoned it was the most plausible way to get out of the atmosphere and avoiding the UV depletion that otherwise results. While in Boston, he also visited the Massachusetts Institute of Technology, the then President of which was Karl Taylor Compton. Returning to Europe, he attended an international conference on nuclear physics in the Niels Bohr Institute in Copenhagen. This was instrumental in shifting his focus to nuclear science later. After his long but intellectually fulfilling tour, Saha returned to Allahabad in 1937. In 1938, he organised a symposium on "Power Supply" under the auspices of the Academy, and requested Nehru to inaugurate it. Though at that point of time, Nehru and Saha shared a cordial relationship, it later turned sour, which considerably hindered the plans and propositions he wanted to advocate to employ nuclear science to public benefit.
During his time in Allahabad he rederived Dirac's quantisation condition for magnetic monopole.^[4] Dirac was one of the first scientists to devote considerable attention to the study of magnetic monopole. This led Saha to the observation that a particle could in principle have both electric charge and magnetic charge. Such a particle (hypothetical) would be called a dyon. This quantisation condition on its charges as derived by Saha turned out to be an elegant generalisation of the principle proposed by Dirac.^[16] Around this time, he felt constricted in Allahabad, and feeling that Calcutta would provide better opportunities to disseminate science, he returned to Calcutta in 1938.

In Calcutta

Saha returned to the Calcutta University in July 1938. He became the Palit Professor and Head of the Department of Physics. At that time Shyama Prasad Mukherjee was the Vice Chancellor of the University and who was soon to be succeeded by Sir Mohammad Azizul Haque. After joining Saha immediately got involved in organizing research in the Palit Laboratory. He also took the task of remodeling the MSc syllabus in physics. Saha later introduced a general and a special paper in nuclear physics and a general paper in quantum mechanics in 1940.

Institute of Nuclear Physics

As mentioned earlier, Saha's interest in nuclear physics was aroused during his foreign trip in 1936-37. Impressed particularly by what he saw at Berkeley, he sent in 1938 his student B.D.Nag Chowdhary to Berkeley to study and work under Lawrence, and learn all he could about the cyclotron. Saha was keen to have a cyclotron in the Calcutta University and used his influence with Nehru to persuade the Tatas to give him a grant to build one. The Tatas obliged with Rs. 60,000/- which wasn't however sufficient to construct a cyclotron. In 1941 Nag Chowdhary returned, and thanks to his efforts in America, a consignment of cyclotron parts (mainly for making the magnet) soon followed. Meanwhile America entered the war and the ship carrying the next batch of equipments (mainly vacuum pumps) was sunk by the Japanese. This was major setback, and now there was no hope of getting any parts from America; anyway, American scientists, Lawrence included, had drifted towards the Manhattan Project. The parts now all had to be made in Calcutta, and this proved to be an interminable affair. Eventually it took many years to complete (it started working after Saha passed away). Apart from this Saha also started on a modest scale some cosmic-ray observations in Darjeeling. The event of the atom bomb dropping on Japan made Saha further aware of the profound importance of nuclear energy. So he resolved to establish an autonomous institute under the umbrella of the university devoted exclusively to the study of nuclear science and its prospects. As a result the Saha Institute of Nuclear Physics came into being in 1948. It was declared open by Irène Joliot-Curie in 1950. As per the university regulations, Saha had to retire in 1952 both from the Palit Professorship and the post of the Director of the Institute of Nuclear Physics. However he retained links with both the institutes in honorary capacity.

Indian Association for the Cultivation of Science

Right from the early thirties Saha was deeply interested in the IACS. In 1944 he became its Honorary Secretary, and following the death of the president in 1946, himself became its president. At that time the IACS was located in Bowbazar. Following the golden era in which Raman conducted his research there, the institute sort of plodded on, and Saha was keen to inject a fresh life into it by starting several new research programmes. all this took time and money, and eventually he persuaded the Government of West Bengal to shift the institute to Jadavpur after buying ten acres of land there. Obeying the Association rules, Saha stepped down as president in 1950. Meanwhile Shanti Swaroop Bhatnagar, with whom he had maintained a cordial relation since meeting him in London in 1920, suggested that it was time that the IACS had a full time director. He further insisted that the post be offered to Saha so that he could complete the reorganisation work he had started earlier. Thus in 1953, Saha became the first director of IACS, a post he held till his death in 1956.

Saha and Atomic Energy

Saha was aware of the electrifying discovery of nuclear fission by Hahn and Meitner in 1939 and the stupefying possibilities this discovery was pregnant with. Meanwhile in 1940 the British rulers in Delhi formed a Board for scientific and Industrial Research (BSIR) with Bhatnagar as the head. Saha was invited to be a member. In 1942, the Government constituted a superior body called CSIR where once again Saha was made a member.
By 1944 it became clear that the tide of fortune in the war was turning against Germany and Japan. In anticipation of victory, the British Government began to make plans for post-war reconstructions. As a part of the process, it asked the Royal Society to send Prof. A.V. Hill to India to advise the government. Hill came and met many scientists, Saha included. He then recommended that an Indian Scientific Mission (ISM) be sent abroad to observe scientific and industrial progress and make post-war plans. The recommendation was accepted and a delegation left India in October 1944; Saha was a member of the ISM.
The tour took the mission to several countries including America. While there, Saha made enquiries about research on atomic energy but drew a blank. He did not know it right then that the Manhattan Project was going on in full swing and atomic energy research was the most closely guarded secret. His enquiries prompted the FBI to interrogate him to gather how much he really knew about their project. However they were relieved that he knew nothing, though his knowledge and expertise on the matter astounded them. On return to India the ISM prepared an official report and submitted it to the Government; the report was drafted by Saha. In 1947 India became free and Nehru became the Prime Minister of India. Atomic energy was the new hope and as member of the BSIR, Saha had every reason to hope that he would be able to play a key role in the development of atomic energy in India. Bhabha also had similar thoughts and he too began to offer Nehru ideas on the subject. In 1948, Saha was formally asked by the Government of India at Nehru's insistence about the formation of Atomic Energy Commission which Bhabha had suggested. Saha firmly opposed the idea on the grounds that India lacked the required industrial base to augment it, and that trained manpower was not available. In his view, before launching a full-fledged atomic energy programme, the industry ought to build up first, and Nuclear physics-oriented courses should be introduced in various universities to obtain a competent manpower. He strongly advocated the French model of atomic energy development which was in fact the brainchild of his friend Frédéric Joliot-Curie. Bhabha, on the other hand, was a proponent of a much faster and more vigorous programme of development which appealed to Nehru. As a result the Atomic Energy Commission was set up in 1948 and the Atomic Energy Establishment, Trombay in 1954.

Saha and calendar reform

Saha's work relating to reform of Indian calendar was very significant. Saha was the Chairman of the Calendar Reform Committee appointed by the Government of India in 1952 under the aegis of the Council of Scientific and Industrial Research. Other members of the Committee were: A. C. Banerjee, K. K. Daftari, J. S. Karandikar, Gorakh Prasad, R. V. Vaidya and N. C. Lahiri. It was Saha's effort which led to the formation of the Committee. The task before the Committee was to prepare an accurate calendar based on scientific study, which could be adopted uniformly throughout India. It was a mammoth task. The Committee had to undertake a detailed study of different calendars prevalent in different parts of the country. There were thirty different calendars. The task was further complicated by the fact that with calendar religion and local sentiments were involved. Nehru, in his preface to the Report of the Committee, which was published in 1955, wrote: "They (different calendars) represent past political divisions in the country…now that we have attained Independence, it is obviously desirable that there should be a certain uniformity in the calendar for our civic, social and other purposes and this should be done on a scientific approach to this problem." Some of the important recommendations of the Committee were:

1. The Saka era should be used in the unified national calendar. (The year 2002 corresponds to the Saka era of 1923-24.)
2. The year should start from the day following the vernal equinox (occurs about March 21) day.
3. A normal year would consist of 365 days while a leap year would have 366 days. After adding seventy-eight to the Saka era, if the sum is divisible by four, then it is a leap year. But when the same becomes a multiple of 100 it would be a leap year when it is divisible by 400, otherwise it would be a common year.
4. Chaitra should be the first month of the year. From Chaitra to Bhaadra each month would have thirty-one days and the rest to have thirty days.

Saha and river physics

Saha was deeply concerned with the recurring disastrous floods in many Indian rivers. The extensive damage caused by floods in North Bengal in 1923 prompted Acharya Prafulla Chandra Ray to organize relief operation under the aegis of North Bengal Relief Committee. Ray was able to collect a large fund from the general public for the relief work and he was assisted by Subhash Chandra Bose, Meghnad Saha and Satish Chandra Dasgupta. And it was while carrying out the relief work Saha got a first hand experience of the devastating power of floods. Saha wrote about his experience in newspapers and magazines. In his Presidential address to the Indian Science Congress in Mumbai in 1934 he drew specific attention to serious problems caused by floods. He also emphasized the need for a River Research Laboratory. Again in 1938, in his presidential address to the National Institute of Sciences he made this topic the theme of his discourse and highlighted the danger posed by recurrent floods in Indian rivers, particularly in the deltaic ones. After the 1923 flood, Saha witnessed two major floods in 1931 and 1935. In 1943 the flood in Bengal isolated Kolkata from rest of India and Saha wrote extensively on the issue. Saha's writings and speeches made the government realize the gravity of the situation. As a result the Damodar Valley Enquiry Committee came into being in 1943. The Committee was chaired by the Maharaja of Burdwan. Saha was also a member of the Committee. Saha presented a plan for handling the Damodar river system before the Committee. He also wrote extensively on river control based on modern science and technology. He argued that the model of Tennessee river system under the Tennessee Valley Authority (TVA) in United States could be adapted to the Damodar Valley. The Central Government appointed a technical advisory committee in 1945 under the chairmanship of Mr. H.M.Mathews. Another member of the committee was Mr.W.L.Voorduin, who had earlier served on TVA. The committee supported the claims of Saha, and at the instance of Dr. B. R. Ambedkar, the then member-in-charge of power and works in the Viceroy's cabinet, the Government adopted a resolution to set up a Damodar Valley Corporation (DVC) after the model of TVA. The DVC was set up in March 1948.

Death

In early 1956, Saha developed serious health problems on account of high blood pressure. Though his doctors advised him to slow down, he continued with his work. On February 16, he had an appointment with his old friend P.C.Mahalanobis, now a favourite of Nehru and closely associated with the Planning Commission. Enroute to the office he collapsed. He was rushed to the hospital, but he never recovered.

An estimate

Saha was of the opinion that large-scale industrialization was the only answer for improving the quality of life. He thought that India had no hope if she failed to develop science and technology. Saha wrote: "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 indifferent 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 of maldistribution of wealth, due to historical causes, are being rapidly cured by introduction of social laws." Despite his patriotic dispositions, he refrained from participating in the freedom struggle. Family responsibilities compelled him to take a job, and the job he got led him to the ineffable world of science. Becoming absorbed in research he then entered what is colloquially called the ivory tower. However his withdrawal was temporary and he slowly drifted out. As he once put it: "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.".^[17] In 1952 Saha was elected Member of the Parliament as an independent candidate from the North-West Calcutta constituency. It was at the request of Sharat Chandra Bose that he decided to stand as a Indian National Congress candidate from Calcutta. Although there were rifts between him and the Congress because he had persistently spoken against charka and khaddae which would be the cardinal points of Congress activity. However this did not prevent him from defeating his nearest Congress rival by an overwhelming margin. Welcoming Saha's election JBS Haldane said: "May I also be allowed to congratulate him on his recent successful reentry recently into politics. India (and Britain too) needs men who will bring some understanding of science to the government of the country. Even those who do not share his political views may rejoice that he can make his voice heard in the council of the people." He was nominated for the Nobel Prize in Physics four times- 1930, 1937, 1939, 1940.".^[18] It is said that the prize committee was of the opinion that one winner in a century from India was more than what Physics could tolerate.

Tributes to Saha

• "Meghnad Saha's ionization equation (c. 1920), which opened the door to stellar astrophysics" was one of the top ten achievements of 20th century Indian science [and] could be considered in the Nobel Prize class." - Jayant Vishnu Narlikar^[19]

• "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^[20]

• "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^[21]

• "It is a pleasure to have the opportunity of congratulating you on the occasion of your sixtieth birthday for your outstanding achievements, especially in the field of thermodynamics. As you know, I at one time had the honour of nominating you for the Nobel Prize for your work in the area..." - Arthur Compton"^[22]

• "I still remember with great pleasure the inspiration that I received from reading Professor Meghnad Saha's fundamental contributions to the theory of gas ionization..." - Enrico Fermi"^[22]

• "I well remember how, on the publication of his early and important paper on ionisation in stellar atmosphere, the late Professor Alfred Fowler drew my attention to it and emphasized its fundamental importance. And so it proved, for this paper was the stimulus to the work of Milne, R.H.Fowler, and others in subsequent years. In fact almost all work on stellar atmosphere has been based on it, either directly or indirectly. The paper provided a new method of attack and opened the way to the solution of many problems that had been puzzling." - Harold Spencer Jones"^[23]

• "I have known and admired him for many years. Indeed, I shall never forget the intellectual thrill I derived from learning about "Saha's ionisation equation" in my early days as a graduate student...." - Ernest Lawrence"^[22]

• "The Harvard Observatory owes much to Professor Meghnad Saha. His pioneer work thirty years ago on temperature ionisations in sun and stars inspired the activities of British scientists who in turn inspired the work here at Harvard of Mrs. Cecilia Payne-Gaposchkin, Donald M. Menzel and Frank Hogg; their work established modern astrophysics in Harvard." - Harlow Shapley"^[22]

• "Many years ago when I was a graduate at California, I was working on some things in connection with the ionisation of the alkali metals - a problem which I never succeeded in finishing. In the course of this work I read with great interest your very important publication of that time on the ionisation as it affected the spectra of the star. It was in fact one of the first scientific papers which I read with very great care as a graduate student...I greatly admired this publication and it has been referred to over and over again in the years since..." - Harold Urey"^[22]

References

1. ^ ^{a b} Kothari, D. S. (1960). "Meghnad Saha. 1893-1956". Biographical Memoirs of Fellows of the Royal Society 5: 216–226. doi:10.1098/rsbm.1960.0017.  edit
2. ^ ^{a b} "Meghnad Saha". http://www.saha.ac.in/cs/archive.mns/index.php?pg=3. Retrieved 2010-06-13. 
3. ^ "Meghnad Saha Biography". http://www.calcuttaweb.com/people/msaha.shtml. Retrieved 2010-06-14. 
4. ^ ^{a b c d e f g} "Meghnad Saha". http://www.new.dli.ernet.in/rawdataupload/upload/insa/INSA_1/20005b68_99.pdf. Retrieved 2010-06-13. 
5. ^ ^{a b} "Meghnad Saha". http://www.saha.ac.in/cs/archive.mns/index.php?pg=4. Retrieved 2010-06-13. 
6. ^ "On Radiation-Pressure and the Quantum Theory". http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1919ApJ....50..220S&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf. Retrieved 2010-06-13. 
7. ^ Venkatraraman,G. (1995). Saha And His Formula. University Press. p. 57. 
8. ^ "The Stationary H- and K-lines of Calcium in Stellar Atmosphere". http://www.nature.com/nature/journal/v107/n2694/pdf/107488a0.pdf. Retrieved 2010-06-13. 
9. ^ ^{a b} "Meghnad Saha". http://www.banglapedia.org/httpdocs/HT/S_0022.HTM. Retrieved 2010-06-14. 
10. ^ On a Physical Theory of Stellar Spectra. JSTOR 93980. 
11. ^ "Meghnad Saha". http://www.vigyanprasar.gov.in/scientists/saha/sahanew.htm. Retrieved 2010-06-13. 
12. ^ "Meghnad Saha". http://www.answers.com/topic/meghnad-saha. Retrieved 2010-06-13. 
13. ^ ^{a b} "Meghnad Saha". http://www.banglapedia.org/httpdocs/HT/S_0022.HTM. Retrieved 2010-06-14. 
14. ^ "History of INSA". http://insaindia.org/history.htm. Retrieved 2010-06-13. 
15. ^ "A Stratosphere Solar Observatory". http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1937BHarO.905....1S&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf. Retrieved 2010-06-13. 
16. ^ "Meghnad Saha". http://www.stealthskater.com/Documents/Monopole_02.pdf. Retrieved 2010-06-13. 
17. ^ "Meghnad Saha". http://www.vigyanprasar.gov.in/scientists/saha/sahanew.htm. Retrieved 2008-05-31. 
18. ^ "Meghnad Saha". http://rsnr.royalsocietypublishing.org/content/61/3/333/T1.expansion.html. Retrieved 2010-06-13. 
19. ^ Narlikar, Jayant (2003). The Scientific Edge. Penguin Books. p. 127. 
20. ^ Rosseland, S. (1939). Theoretical Astrophysics. Oxford: Oxford University Press. http://www.vigyanprasar.gov.in/scientists/saha/sahanew.htm. 
21. ^ Kothari, D. S. (1970). Biographical Memoirs of Fellows of the National Institute of Sciences of India. 2. New Delhi. http://www.vigyanprasar.gov.in/scientists/saha/sahanew.htm. 
22. ^ ^{a b c d e} Venkatraraman,G. (1995). Saha And His Formula. University Press. p. 188. 
23. ^ Venkatraraman,G. (1995). Saha And His Formula. University Press. p. 190. 

Further reading

• Obituary - The Observatory 76 (1956) 40
• Obituary - Proceedings of the Astronomical Society of the Pacific 68 (1956) 282

External links

• "Meghnad Saha". http://www.vigyanprasar.gov.in/scientists/saha/sahanew.htm. Retrieved 2008-05-31. 
• Biography
• Chitra Roy on her father
• Biography
• ScienceWorld: Saha Equation
• List of M. N. Saha's papers

Persondata
Name	Saha, Megh Nad
Alternative names
Short description	Indian physicist
Date of birth	6 October 1893
Place of birth	Shaoratoli, Dhaka (Present day Bangladesh)
Date of death	16 February 1956
Place of death