C.V. Raman and the Colour of the Sea

“The view has been expressed that the much admired dark blue of the deep sea has nothing to do with the colour of water, but is simply the blue of the sky seen by reflection … Whether this is really true is shown to be questionable by a simple mode of observation used by the present writer, in which surface-reflection is eliminated, and the other factors remain the same.”

On November 17, 1921, Chandrasekhara Venkata Raman (1888-1970) sent a letter concerning ‘The Colour of the Sea’ to the journal Nature. He was on his way back from his first visit to England on the SS Narkunda, commissioned only the year before by the Peninsula and Oriental Steam Navigation Company. Raman sent the letter as the ship docked in the Bombay port, finally disputing Lord Raleigh’s claim following his own voyage around the African continent, that “the much admired dark blue of the deep sea has nothing to do with the colour of water, but is simply the blue of the sky seen by reflection” (Colours of Sea and Sky, March 10, 2010).

Five years into his first academic appointment, Raman had travelled to England for a few months to attend the Second Congress of the Universities of the Empire (July 5-8). Barely two months after the publication of this letter, Raman was nominated to a fellowship of the Royal Society – the fourth Indian and the second physicist to be nominated (the first physicist was Jagadish Chandra Bose).

At the time, Raman was most known for his work in acoustics but his interest in optics and the scattering of light was already established, in fact, in his very first letter to Nature (Newton’s Rings in Polarised Light, 7 October 1907). How did this recognition come to be?

Raman is the only Nobel Laureate in science of Indian origin who studied, worked and continued to live in the country his entire life. He may be said to be exceptional in another way: he was an experimentalist! He was awarded his first two degrees by the University of Madras and following his MA, he immediately joined the Indian Finance Services. He was appointed as assistant accountant general and posted in Kolkata in 1907. In fact, his first letter to Nature, mentioned earlier – correcting an observation in Thomas Preston’s ‘Theory of Light” – was written from the ‘Science Association Laboratory, Calcutta’.

Why was an accountant writing from a ‘science association laboratory’?

In Kolkata, Raman began working after hours on physics experiments in a public laboratory for the natural sciences – an institution of a kind that is today no longer available for research outside established academic or industrial laboratories. The Indian Association for the Cultivation of Science (IACS) was established by the physician Mahendralal Sircar in 1876 with the goal to “cultivate science in all its departments with a view to its advancement by original research and with a view to its varied application to the arts and comforts of life.”

Equipped with laboratory facilities, the association opened its doors to those with an interest to conduct research and offered lectures by the best minds in the city. Among others, Sir Asutosh Mukherjee, also an accomplished lawyer and later vice-chancellor of the University of Calcutta, lectured in mathematics. He became one of Raman’s promoters at the IACS, and ten years later, supported his move to the newly established University Science College (USC).

In less than ten years of his arrival in Calcutta, Raman held the Palit Chair in physics at the USC at a salary lower than he drew as a civil servant, but with access to his own laboratory, and students and research scholars to work with. Interestingly, Raman continued to work at the IACS laboratories as well as offer public lectures alongside his work at the USC. It was an institution he stayed in close connection with, even if not always without conflict, until his move to the Indian Institute of Science, Bengaluru, 17 years later. Of his 23 years in Kolkata, Raman was an accountant and an evening-researcher for ten, but he kept working at the IACS laboratories for over two decades.

It is worth noting that Raman’s research and move to a full time research career was made possible by philanthropy in both cases: the IACS was carefully established in the 19th century with donations from landed aristocracy and with recognition from but no control of the imperial government. About four decades later, fuelled by the National Education Movement after the partition of Bengal, the University Science College was established with generous donations from the barrister Sir Taraknath Palit and jurist Sir Rashbehari Bose.

On his first journey to England, Raman carried with him a pocket-sized spectroscope and a Nicol prism, and he made observations on the Mediterranean, the Red and the Arabian seas. All along the way he was looking to answer one question: ‘What is it that diffracts the light and makes its passage visible?’ As he made progress in the journey, he began to publish letters in Nature: from an address in Putney, he wrote three letters in a build-up towards his concluding observations: ‘The Colours of Breathed-on Plates’ (August 4), ‘The Radiant Spectrum’ (September 1), ‘Smoky Quartz’ (September 15), and a fourth from the port of Aden on his way back to India, on ‘A Method of Improving Visibility of Distant Objects’ (October 20).

Two of the letters engage directly with Lord Rayleigh’s theory of the elastic scattering of light – a phenomenon now known as Rayleigh scattering – to explain why the sky is blue. While the two letters build upon the observable claims in Rayleigh’s theory, in the fifth he claims that Rayleigh’s claim falls short.

Observing water over three seas with a simple Nicol prism, Raman concluded that water molecules scatter light just like air molecules do. Light scattering in air was Rayleigh’s explanation for why the sky was blue; and Raman found that this was true also for why the sea was blue. Interestingly, Raman’s fourth letter simply detailed the usefulness of the Nicol prism, a method already in use since World War I, proposed by David Wilson-Barker in ‘A Manual of Elementary Seamanship‘. Small science could still move frontiers at this time, something that would change near completely after World War II.

Back in Calcutta in the following week, he commenced correspondence in a series of letters starting with ‘The Molecular Scattering of Light in Liquids and Solid’ (November 24), connecting his insight on the colour of the sea with quantum theory, all while deepening his study with 60 different common liquids. For most, quantum science is for the most part theoretical and abstract. We find with Raman not only an experimental inquiry but one approached from curiosity that began with an observation: why is the sea blue?

In the end, Raman’s colleague Kariamanikkam Srinivasa Krishnan (or K.S. Krishnan) found that scattered light was polarised – which was, again, published in Nature. Following this, Raman began to measure the exact wavelengths of the incident and scattered light using a spectroscope that is still held at the IACS laboratories. Eventually, this work led to a Nobel Prize for Raman in 1930, making him the first Asian to be thus recognised in science.

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I wanted to explore Raman’s way of doing science through one paper that he wrote about the colour of the sea. He looked at his first voyage across the seas as an opportunity to experiment with simple equipment and a determination to verify Rayleigh’s claim made on a voyage taken a decade before his own. He was barely five years into his first academic appointment but he held a chair professorship. This was possible because of a public laboratory where he pursued his experiments  and published continuously for a decade even as he held a different day-job. He published enough to be recognised for a fellowship of the Royal Society. I have not included here the other papers and communications that Raman sent to leading European journals during this short period of his trip to England. One of them was even about the whispering-gallery phenomenon at St. Paul’s cathedral!

Raman’s work was recognised to be both strong and important enough that he was awarded the Nobel Prize within two years publishing his paper on the so-called Raman effect. He was not the only Indian to be nominated for the award in those years, however; Meghnad Saha – his colleague and at times adversary – came very close after being nominated thrice, but an astrophysicist was not physicist enough for the committee deciding on the prize in the 1930s.

It is a pity that we are yet to see a robust biography of this tenacious, querulous, and meticulous intellectual. The absence of his story, among others, impoverishes not only the history of science in India but also our ability to understand and debate contemporary science in India.

Jahnavi Phalkey is a historian of science, filmmaker and founding director, Science Gallery Bengaluru.

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