S. C. SIRKAR, C. V. RAMAN AND DIFFUSE SPOTS IN LAUE ... Rajinder Singh.pdf · C.V. Raman in 1926; and did D.Sc. at the University of Calcutta. In 1940, C.V. Raman and his students

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S. C. SIRKAR, C. V. RAMAN AND DIFFUSE SPOTSIN LAUE PHOTOGRAPHS

RAJINDER SINGH*

Sukumar C. Sirkar was the first person in India, who started measuring the intensity of Ramanlines, shortly after the discovery of the Raman effect in 1928. He began his research carrier underC.V. Raman in 1926; and did D.Sc. at the University of Calcutta. In 1940, C.V. Raman and hisstudents in Bangalore announced the discovery of a new kind of Laue spots in crystals. This led tocontroversy over the discovery, as well as theoretical interpretation of the effect. The present articleshows the role played by Raman’s students K. Banerjee, K.S. Krishnan and S.C. Sirkar in thecontroversy.

ARTICLE

* Research Group – Physics Education and History of Science,Institute of Physics, University of Oldenburg, Germany.e-mail: [email protected]

Introduction

SC. Sirkar (Figure 1) is an unsung hero of IndianScience. His life story and relation with Ramanare explored elsewhere by the present author. In

contrast, India’s only Nobel Laureate in the field of naturalscience, C.V. Raman, is a well-known figure. There are anumber of articles and biographies which deal with variousaspects of his life. However, none of them explore the roleplayed by Raman’s Bengali students K. Banerjee and S.C.

DOI: https://doi.org/10.36094/sc.v85.2019.SCSirkarandCVRaman.Singh.373

Sirkar, in the controversy on the observation of diffuseLaue photographs, which were observed by Raman andhis students in the 1940. The present communicationintends to fill the gap.

Observation of “Raman Reflections” in LauePhotographs and Raman-Nath Theory

Background - Study of Crystals and Diffuse Spotsin Laue Photographs

The discovery of x-rays by Wilhelm Conrad Röntgen,Germany, led to a “revolution” not only in medicine butalso in many other fields of science. Shortly after thediscovery, the first experiment was performed in India atthe IACS.1 In 1901, the first Physics Nobel Prize wasawarded to the discoverer.2

In 1912, the German physicists, Max von Laue, W.Friedrich and P. Knipping, established the fact that a crystaldiffracts x-rays.3,4 Nearly at the same time the Britishphysicists W.H. Bragg and W.L. Bragg showed thatreflected x-ray pattern obtained in a Laue-photograph ischaracteristic of the crystal.5 In 1914, Peter Debye, atheoretical physicist and physical chemist, predicted theexistence of diffused spots in Laue photographs caused bythe thermal vibration of atoms in crystals.6 These spotswere observed by W. Friedrich.7,8,9 Hilding Faxén10-11 andIvar Waller12-13 of Sweden, provided theoretical explanation

Figure 1: Prof. S.C. Sirkar with Prof. Wolfgang Kiefer, University ofWürzburg, Germany (1978). Credit: Prof. Wolfgang Kiefer.

374 SCIENCE AND CULTURE, NOVEMBER-DECEMBER, 2019

of the position and intensity of the background scattering.,As the diffuse spots had no application in any field ofresearch, it remained obscured for the next two decades.In 1940, India’s Nobel Laureate C.V. Raman announced anew discovery, which brought the diffuse spots at thecentral point of research in crystallography (detail below).

“Discovery” By Raman and His Students

In 1940, C.V. Raman and P. Nilakantan observed “anew x-rays effect” in crystals (Figure 2). They suggestedthat the unmodified reflection is associated with the normalstructure of the crystal, whereas the modified reflectionscome into existence due to the vibration of the crystallattice, which is quantum mechanically excited by theincident x-rays.14

Figure 2: A, B, and C are marked as points in Laue photographs atwhich the new effect was observed by C.V. Raman and P. Nilakantan.Courtesy: “Current Science.”

To explain the observations, Raman and his studentN.S.N. Nath gave the following equation: 2d sin ψ sin (θ± ε) = nλ sin θ, where, d - the crystal spacing; n = 1, 2, 3,…; 2 ψ – the angle between the reflected and incident x-rays; ε – inclination of the dynamic stratifications to thestatic crystal planes; and θ – the inclination of the phaseswaves of the lattice oscillations to the static crystal planes.15

More extensive version of Raman’s experimental andtheoretical results was published in the “Proceedings ofthe Royal Society London.” Therein Raman wrote: (i) Themodified scattering is due to the excitation of the elasticsolid or low frequency vibrations of the crystal lattice bythe X-ray photon. (ii) The quantum reflexion is due to theexcitation of the infra-red or characteristic high frequencyvibrations of the crystal lattice by the X-ray photons.16 In

the second paper Raman showed that his theory canexplain the following observed phenomena in diamond:

“(1) the specular character of the quantum reflexionfrom the (111) planes, (2) the geometric law of suchreflexion and especially the fact that, in general, thereflexion falls outside the plane of incidence, (3)the subsidiary features accompanying the reflexion,viz. faint elliptic spots and elongated streamersnoticed in certain special cases, (4) the absoluteintensity of the reflexion which is an appreciablefraction of the intensity of the classical reflexion,(5) the failure of the (110) planes to exhibit similarreflexions, (6) the persistence of the reflexions bythe (111) planes with undiminished intensity at liquidair temperature and the relatively small increase ofintensity at high temperatures, and (7) theappearance of a diffuse scattering having anundiminished intensity at low temperatures.”17

And further:

“The differences between diamond and other crystalsin respect of these X-ray phenomena are explainedby taking into consideration the differences in thefrequency and character of their lattice vibrationsin the infra-red region as revealed by thespectroscope.”18

More detailed explanation about the position andintensity was given by Raman’s student, P. Nilakantan(detail later). From the USA, W.H. Zachariasen stated thatRaman and P. Nilakantan reported the presence of weakintensity maxima in Laue photographs. This is not a newphenomenon, as it has been observed by various persons.G.D. Preston, UK, has shown the intensity of these spotsincreases with temperature. He (WHZ) himself, at a meetingof the American Physical Society on Dec. 1, 1939,presented a detailed theory of the effect.19 In “PhysicalReview” he condemned Debye formula for the intensity ofthe diffuse spots and replaced it by a more complicatedexpression. In his theory the intensity of the diffusescattering changes much more rapidly with the scatteringdirection and shows a number of maxima. To calculate theposition of the maxima he gave an expression.20 In thenext publication, he reported that experiments done withrocksalt and Cu Kα radiation confirm his theory.21

In a short article to “Nature” I.E. Knaggs, et al.,reported that C.V. Raman and P. Nilakantan have observeda new type of reflection in diamond with x-rays. Insubsequent articles they presented theories to explain theexperimental results. This cannot be seen as a new

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discovery as Indian authors overlooked the observationof the spots by other workers.22

Raman insisted: “I wish to point out that the existenceof a distinct new type of specular x-rays reflexion of adynamical kind by the lattice planes of a crystal was forthe first time recognised and its physical characterelucidated in the publications from this Institute [Probably,he meant Indian Institute of Sciences] (emphasis inoriginal).”23

Raman’s argument was - Debye’s and Waller’stheories are based on thermal vibrations of atoms. Theyare derived on the basis of classical mechanics. Theypredicted entirely different intensity, geometric position andbehaviour of diffuse spots at low temperatures than thatwas observed by him.24 From theoretical point of view,his criticism was: (i) These theories are based on Born’spostulate of cyclic boundary condition, which is an ad hocassumption as it assumes an infinite crystal, to calculatethe forces of the particles on the surface. (ii) Born’spostulate does not correctly represent the infra-redvibrations of a crystal lattice.

With experimental data Raman proved the correctnessof his theory; and disproved Faxen’s and Zachariasen’stheory for determining the position of diffuse spots in rocksalt.25

Raman’s challenge to the criticism did not remainunanswered. Reaction of the “British Group under theguidance of K. Lonsdale”26 as well as of Max Born arediscussed in detail elsewhere.27 Some of the facts are takenfrom these articles, so that a reader is able to understandthe background of the controversy. In the following section,the present discussion is limited to the reaction of W.H.Zachariasen and Indian physicists.

Controversy Over Diffuse Spots: SCS vs.Raman

S.C. Sirkar et al. published their findings in “Scienceand Culture”. They had the following objections to Raman’swork:

(i) “The displacement of the atoms from their originalpositions required to give the new maxima in the observeddirection is too large to occur actually in the crystal.”28

(ii) “The intensity of the new maxima should not dependvery much on the variation of the angle of incidence fromthe Bragg angle, but actually it depends very much on thisvariation.”29 (iii) “The direction of new diffractionmaximum should make an angle 2θB with the direction ofthe incident X-rays according to the proposed hypothesis,but actually the angle observed is sometimes less and

sometimes greater than 2θB.” (iv) “In the case of diamondthe frequency of the characteristic vibration is such thathv» kT at temperatures below 1000°C and hence thethermal excitation of this vibration is not possible at anytemperature below 1000°C, but actually it is observed thatthe intensity of the new diffraction maxima increasesappreciably in the case of diamond when the crystal isheated to 500°C.”30

Detailed results were published by the authors in the“Proceedings of the National Institute of Science”, India,(today known as Indian National Science Academy). In thatarticle, SCS et al. theoretically calculated the displacementof atoms due to lattice vibration which is of the order of 1x 10-8 cm. According to Raman’s theory it was at least104 times more than this value. Further they argued that ifthe angular displacement of the 111 planes would take placeas postulated by Raman et al.,:

“the amplitude of displacement would have a certaindefinite value, and the intensity of the reflection bythese oscillatory planes would not depend on themagnitude of the variation of the glancing anglefrom the Bragg angle for the reflection of themonochromatic radiation. But actually, the intensityof the new spots is found to diminish rapidly withincrease in the variation mentioned above.”31

They continued:

“In fact, assuming that the Bragg relation holds goodfor the mean position of the planes correspondingto the calculated values of glancing angles anddifferent values of the spacing have been obtained.The reason for this discrepancy is not explained inthe theory put forward by Raman and Nilakantan.”32

They showed that the diffuse maxima observed byRaman and Nilakantan in diamond agreed quantitativelywith Zachariasen’s theory.33 For experimental work, SCSand Gupta studied a number of diamonds. They found thatthe new diffraction maxima due to Cu Kβ lie close to theLaue spots due to 111 planes produced by the whiteradiation; and they were quite intense. In contrast, thosedue to Cu Kα were weaker; and far away from the Lauespots (Figure 3).34

The authors stated that comparison of Raman’s andtheir observed pattern shows that “the directions of thestreamers are along the loops starting from the Laue spotsdue to 111 planes.” Consequently “the planes of reflectionsproducing these streamers are also the planes of incidenceson some planes of the crystal which might be imagined tobelong to these zones but whose indices are verycomplicated.”


In 1941, Raman’s student, P. Rama Pishatory in hispaper “On the geometry of the quantum reflection of x-rays in diamond” extended the Raman-Nath formula. Hispaper deals with the Raman reflections from the (111)planes of diamond. He contrasted the round shaped Ramanspots with the elliptical shaped Laue reflections andexplained them with his geometrical theory (Figure 4).35

According to Pisharoty’s theory the quantum reflectiontakes place whenever the vectors τ1, τ2 and τ3 touch or cutthe sphere of reflection.

Figure 4: “Streamers” and “subsidiary spots”. τ1, τ2 and τ3 – Threereciprocal phase vectors. τ1 is in the plane of incidence. The diagramrepresents the case θi › θB, that is, glancing angle is greater than Braggangle. R1, R2 and R3 are Raman spots; and L is the Laue spot. Credit:Indian Academy of Sciences.

To Pisharoty’s results, SCS and B.M. Bishui opined:

“Reflection can take place only when the ends ofthese vectors come on the sphere of reflection.Hence it is implied in Pisharoty’s arguments thatthe magnitudes of τ1, τ2 and τ3 are continuouslyvariable having values ranging from zero upwards.τ1, τ2 and τ3 can however, have such small values

Figure 3: Laue photograph in diamond. Left: Due to white radiationfrom W target. Right: Due to radiation from Cu target. The markedspots are due to new diffraction maxima. Credit: Proc. INSA.

only for the acoustic branch and not for the opticalbranch of vibrations. Again, the acoustic wave vectorin a general direction will have the same effect asits three resolved parts τ1, τ2 and τ3 along the cubeedges. Thus indirectly and aware Pisharoty hasdeduced the geometrical relationship in the case ofdiffuse scattering (emphasis in original) and not inthe case of quantum reflection.”36

According to their opinion Pisharotry’s theorydemands that “when θi = θB, four streamers should form asymmetrical cross with the Laue spot at its middle and theangular length of each streamer should be about twice thedivergence of the incident beam.” They studied Lauephotographs in diamonds and found that in some specimensthe streamers were missing. Further they found: “when thecross section of the incident beam is less than that of thecrystal and θi < θB the diffuse spot is of triangular shapewith its apex towards the Laue spot and not circular asindicated by Pisharoty’s theory.”37

In 1942, in the “Proceedings of the National Instituteof Sciences”, SCS and B.M. Bishui after giving a shorthistory of the diffuse spots, discussed the followingobservations of different scientists: (i) “The position ofextra spots.” (ii) “Origin of the triangular spot and streamersaccompanying the diffuse maximum due to 111 plane ofdiamond.” (iii) “Intensity of the extra spots.” (iv) “Theorigin of the halo around the direct beam” and (v)“Influence of temperature on the intensity of extra spots.”38

They observed Laue pattern in a thin and a thicker crystalof diamond with a short exposure time, as shown in Figure4. The intensity of spots in both the cases is more or lessthe same. “This fact shows that the influence of absorptionand secondary extinction is quite appreciable in the caseof the thicker crystal”.

Figure 5: The Laue pattern in diamond with a thin (left) and thick(right) crystal. Credit: INSA.

Figure 6 shows the measurement with the samecrystals (thin and thick) with longer exposure time. The

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diffuse maximum accompanying the Laue spot due to aparticular plane is more intense in the case of thicker crystalthan in the case of thin crystal. “Thus the ratio of theintensity of the diffuse maximum to that of thecorresponding Laue spot is larger in the case of the thickcrystal than in the case of the thinner crystal”, wrote theauthors. With their results they supported Zachariasen’stheory; and contradicted C.V. Raman’s School of thoughton the theory of quantum reflections.

Figure 6: Laue photographs with longer exposure. Credit: INSA.

It seems that Raman did not take Sirkar’s criticismseriously, as he engaged himself in “fighting” against MaxBorn and K. Lonsdale. However, Raman’s one Bengalistudent Kedareswar Banerjee contradicted Sirkar (detailbelow).

Diffuse Spots and K. Banerjee’s Reaction

K. Banerjee (Figure 7) was one of Raman’s Bengaliassociates. He became the second M.L. Sircar Professorof Physics at the IACS, after K.S. Krishnan left forAllahabad. He was loyal to Raman and he alwaysappreciated Raman’s effort for promoting the IACS. At the80th anniversary of the Raman effect he recalled: “As the

Association was not affluent in those days, he (Raman)ungrudgingly met deficits of the Association from hispersonal Bank Account on several occasions.”39

We have seen above that in the beginning of the 1940sthe controversy over the discovery of the “modified” spotswas on its peak. At the IACS work was being done underthe guidance of K. Banerjee. In the Annual Report of theIACS for the year 1943, under “Discovery by of new-typeof sharp reflection”, it was reported that it is expected thatthe new spots will throw considerable light on the irregularstructure of crystals.40 In a letter to “Nature” K. Banerjeeand C.R. Bose concluded that K. Lonsdale’s idea that thesecondary spots are due to strain is untenable.41 Banerjeeclaimed to have observed a “new effect.” Banerjee was ofthe opinion that spots observed by C.V. Raman, and K.Lonsdale and H. Smith in the case of diamond are same,while the spots observed by him and associates in the casesof phloroglucine dehydrate and benzyl are of new kind.42

K. Banerjee’s associate R.K. Sen continued theinvestigation of extra-Laue reflections in benzyl andcompared the relative intensities of the spots with theabsolute intensities of the NaClO3 crystals at differenttemperatures.43

C.R. Bose, who was working at the University ofDacca sent a paper to the Proc. Indian Nat. Sci. Inst., whichwas communicated by his teacher K. Banerjee. In the paper,the author thanked Prof. S.N. Bose for taking interest inthe work. In his article, C.R. Bose stated that extra diffusespots which come into play at certain definite orientationsof the crystal with respect to the incident x-ray beam werefirst observed by Raman and Nilakantan in 1940.44

C.R. Bose studied phloroglucine dehydrate crystalsand found secondary type of extra reflections, which aresimilar to that of observed by British scientists Jahn andLonsdale in the case of diamond. “In this case thesecondary reflections can be regarded as a two-dimensionaldiffraction effect arising from breaking of the periodicityalong the c-axis, except that for any reflection for whicheither the h or k index is zero, is absent.”45 Some of hisobservations are shown in Figure 8 and Figure 9. He tookLaue photographs after rotating the crystal through 10degree about the ‘a’- and b-axis so that the x-ray beamwas incident at an angle of the c-axis (Figure 9). Heobserved: (i) The position of the secondary spots remainsalmost same, while Laue spots move over considerabledistance. (ii) The shapes of the spots show variations. (iii)There is gradual decrease of intensities of the spots withthe increase of angle. (iv) The central part of extra spotsis blank. (v) Only the outer part of the crystal producesthe secondary extra reflections.Figure 7: Kedareswar Banerjee (1900-1975). Credit: INSA.


Figure 8: (a) – Laue photograph taken with the x-ray beam along the‘a’-axis with the c-axis vertical. (b) Laue photograph taken with the x-ray beam along the ‘b’-axis with the c-axis vertical. Credit: INSA.

He cut a crystal plate into two triangles. Lauephotographs taken show the secondary extra spots havetriangular shape (Figure 9 – Part c)

C.R. Bose concluded that the:

“reflections have been classed as secondary extrareflections from their parallelism with the secondaryextra reflections from diamond, where in suitableorientation they are sharp spots. … In aphloroglucine dehydrate crystal the two types arepresent in the same crystal. Here the peripheral partshows the effect while the central part does not showit at all.”46

In an article in “Sci. Cult.”, S.C. Sirkar47 questionedthe nature of diffuse spots observed by K. Banerjee’sassociate, C.R. Bose.48 He was immediately rebutted byBanerjee, who stated that the apparent dissimilarity pointedout by Dr. Sirkar will easily disappear if one considers theresults from the standpoint of the reciprocal lattice. Furtherhe stated that the simple explanation given by Sirkar is

Figure 9: (a) Laue photograph when the x-ray beam makes an angle of 10 degree with the c-axis. (b)Diffuse spots in a very small crystal. (c) Secondary spots in the case of a triangular crystal. (d) Lauephotograph taken with a narrow x-ray beam which irradiate only the central part of the crystal. Nosecondary diffuse spots are to be observed. Only primary diffuse spots and Laue spots appear. Credit:INSA.

not enough to explain the observed effects, as “the type ofmisorientation postulated by him would give rise to arcswhich in the ideal dis-orientation of the powder photographwould become circles.”49

Sircar had supported Londsdale’s results. In contrast,Banerjee wrote that the observation of secondary spots indiamond and their explanation given by K. Lonsdale onthe basis of strain in diamonds is also untenable.50 Sirkar’sanswer was published with Banerjee’s article in the“Proceedings of the Nat. Inst. Sci. (India)”. SCS stated thathis argument was based on two points: (i) Spots do notmove appreciably if the crystal is rotated through largeangles. (ii) Probably these spots occur at a particular anglewith the beam. Professor Banerjee’s argument is notconvincing as his student C.R. Bose writes that the spotsdo not move appreciably with the change of angle. To thesecond point nothing has been said in their article.51 Inthe next letter Banerjee disapproved Sirkar’s view by givingtheoretical and experimental results.52

In 1948, the study of secondary reflections in Lauephotographs was continued by R.K. Sen. In the case ofNaClO3, he found that the iso-diffusion surface around thereciprocal lattice points obtained by J. Garrido, does notagree with the thermal theory of H.A. Jahn. He designed aspecial camera to study the effect of low temperature inthe cases of phloroglucine dehydrate and benzyl. “Theinvestigations of the sharp extra spots of phloroglucinedehydrate by M.N. Datta had shown that the amplitudesof the derangement waves which are responsible for thesharp extra spots change vary slowly with temperature. Thiswas in contrast with the thermal theory.”53

As it turned out later, the theories given by differentauthors were too simple to explain the observations. EvenMax Born’s theory was unable to explain the vibration linespectra observed by Raman. In 1953, the explanation wasgiven by his student K.S. Viswanathan. He showed thatthe number of frequencies predicted by Raman’s theory“correspond, in Born’s language, to normal mode

frequencies for which the groupvelocity vanishes. Now groupvelocity can vanish for selectednormal modes either for reasons ofsymmetry or on account of thenature of inter-atomic forces.”54

Nearly at the same time Leon vanHove had shown that the frequenciespredicted by Raman’s theorycorrespond to those frequencies (thenormal modes) which have zerogroup velocity in Born’s theory.55

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Born’s theory found its complete confirmation in 1962.56

Author S. Ramaseshan gave the reasons, namely, (i)Elaborate mathematical calculations were required topredict the simplest of optical and thermal properties fromthe Born theory. After the introduction of computer itbecame easy to solve such problems. (ii) “Lacking thenotion of singularities in the spectrum, again not to comefor a decade, the sharp features seen in the Ramanscattering found no explanation.”57

To close with the story of the controversy, in thefollowing section we shall see how Raman was confrontedin his own country by Western scientists, who weresupported by K.S. Krishnan and D.S. Kothari.

K.S. Krishnan, C.V. Raman and thePublication of R.E. Peierls’s Article in India

Raman’s theory predicted discrete frequencies,whereas according to Born’s theory the spectrum wassupposed to be continuous.58 Raman had stated that othertheories are wrong, as they rely on Born’s theory, whichcontains cyclic boundary condition hypothesis, which hasno experimental validity. In order to defend his theory, M.Born sought support from M. Blackman, UK. In “Nature”they wrote that Raman calculated his data of specific heatby superimposing a few Einstein’s functions. They arguedthat cyclic condition was a reasonable approximation— amethod well accepted by mathematicians.59 In order toconvince the readers that Born’s views are correct, hesought experts’ opinion. For instance, he contacted themathematician Walter Ledermann of St. AndrewsUniversity, who supported Born’s views on the cyclicboundary condition, by writing articles in British journal.60-

61 However, E. Schrödinger, the founder of the wavemechanics, expressed his helplessness in this matter. OnMarch 2, 1942, he wrote to Born: “This cyclic business ismerely a technical device, not a physical assumption, toany person who understands the matter it is not doubtful,that it changes nothing, - from a very rigorous mathematicalpoint of view an entirely clear-cut proof might be desirable.…I have also thought about your “cyclic question”, butwithout much result.”62 Western men of science, includingBorn, gave much importance to Raman’s observations asthey were of the opinion that Raman is an excellentexperimental physicists and his observations can hardly bewrong. For instance, on March 2, 1942, Schrödinger wroteto Born:

“The only interesting argument in R’s paper is theexperimental fact, that the Raman-lines and someother optical indications of the “optical latticefrequencies” are “absolutely sharp.” (I don’t think

that anybody who reads these things will pay muchattention to any other (underlined in original)argument than this). … The corresponding frequencyinterval is so small that it satisfies all therequirements of Raman’s experiments.”63

On April 26, 1948, Born wrote to other theoreticalphysicist, R.E. Peierls, and lamented: “The whole matteris very disagreeable to me because nobody supports me inthis unpleasant dispute, though all privately say that theyare on my side.”64 Peierls promised to confront Raman inBirmingham, “if there is any sign, …, that any appreciablesection of the public is being are confused,…”65 As Ramandid not come, Peierls had no chance of confrontation.66

In 1951, Peierls’ was confronted with Raman at theoccasion of a meeting of the Indian Science Congress atBangalore. Raman gave lecture, criticised Born’s theoryand also demanded the explanation of observed sharp lines.Peierls avoided experimental results, but preferred to reston theoretical arguments.67 After returning back from India,he informed Born about the incident.68 Peierls wrote anarticle based on physical concepts. He informed Born. Thelatter suggested him to publish the article in Indianperiodicals, perhaps even in Raman’s own “Proceedingsof the Indian Academy of Science”.69 Peierls wrote toRaman, and proposed to make all possible changes, if thereis anything unclear.70 Raman replied that his results ondiamonds are in disagreement with the theory based oncyclic postulate. He opined: “I am not prepared withoutfurther study to suggest that there is any mathematical errorin the treatment of the problem given in your note. Whatseems to me at the moment more likely is that the physicalassumptions underlying the analysis do not correspond withreality.”71

After Raman rejected the publication, Peierls soughtfor an alternative; and managed to publish the paper in the“Proceedings of the National Institute of Sciences, India”(detail below).

If we rely only on the scientific publications, we see,that not all Bengal based physicists opposed Raman’s idea.Only SCS and his students. They were supported by M.N.Saha, who communicated their papers. Peierls’ paper wascommunicated by D.S. Kothari, a loyal student of M.N.Saha. This would perpetuate the belief that “Bengalis”opposed Raman. However, Peierls’ correspondence offersa surprise; and shows, “Bengalis” were not always and onlyRaman’s opponents. Internally, Raman’s most loyal student,K.S. Krishnan played important role and “supported”Kolkata group. However, it is not my conclusion thatKrishnan was a detractor. My interpretation of the story is


that Krishnan, as a renowned physicist, looked only tothe scientific merit of a paper.

On Oct. 9, 1953, in a letter Peierls asked Krishnan’shelp in publishing the article in India.72 Peierls wasinformed by Krishnan that Prof. D.S. Kothari, the Secretaryof the National Institute of Sciences of India, “has kindlyagreed to communicate it for publication in the“Proceedings of the National Institute of Sciences” and thepaper will appear in the February or March issue of 1954.73

Indeed, Peierls’ article “Note on the vibration spectrum ofa crystal” was published. He wrote the purpose of his articleas follows: “Present a simple proof of the rule usually givenfor obtaining the spectrum of normal frequencies of crystal.The rule is that the distribution of frequencies is the sameas those of a hypothetical crystal satisfying the ‘cyclicboundary condition.’ We shall in the following refer to thehypothetical case as the ‘mathematical crystal’.”74 In thenext step he told the limitations of his model:

“(a) it is not claimed that the normal modes (emphasisin original) of the mathematical crystal are identical withthose of the real model. (b) It is not claimed that the exactvalues of the frequencies are the same in both the cases,but merely that the distribution, i.e., the average numberin a frequency interval Δω large enough to contain manyfrequencies in the same in the two cases to the leadingorder in N, where N is the linear dimension of the crystalin terms of the lattice spacing. Our argument will beformulated to cover three dimensions and the presence ofseveral atoms in the unit cell.”75

Peierls showed that for a crystal dimension of 1 cubiccentimeter, the frequency resolution of approximately 0.01%would be needed to detect effects due to the breakdownof cyclic conditions, and experiments are never done withsuch precession.76

Neither Raman nor his students were not hard coretheoretical physicists. Thus, they did not saw any flaw inPeierls’ conclusions. In 1961, H.B. Rosenstock ontheoretical grounds observed that Peierls’ proof isdependent on the assumption that a disturbance startingfrom a point at a given distance from the nearest surfacewill propagate in the same manner as in an infinite crystalfor a time less than that of the ratio of distance to themaximum velocity of sound. This statement is correct onlywhen the interactions are of short range. For a long-rangeinteraction, infinity, or more precisely the velocity of lightwould have to be substituted for the velocity of sound.Thus this proof also fails to establish a relationship betweenthe behaviour of the finite lattice and the lattice with cyclicboundary conditions when long-range forces occur.77

Born-Raman dispute was finally settled in 1962; afterthe experiments gave the final proof for the correctness ofBorn’s theory, which contained cyclic boundary condition.78

Conclusions

From the forgoing we see that not all “Bengalis”opposed C.V. Raman in the 1940s due to the differencesof views on the observations of diffuse spots in Lauephotographs. Even S.C. Sirkar et al. (whose papers werecommunicated by M.N. Saha, University of Calcutta) andK. Banerjee et al. (whose papers in part were supportedby S.N. Bose, University of Dacca) opposed each other.Raman’s own loyal student, K.S. Krishnan, helped R.E.Peierls in publishing article in Indian journal. In this contextit can be concluded that scientific controversies are a partand parcel of scientist’s life and helpful for the progressof science. However, a particular research group supportshis own people. Consequently, feelings may play role inthe field of rational scientific knowledge.

Observations made by Raman and his students didnot find immediate explanation. This shows theexperimental work done in India was of very high level.

Acknowledgements

I am thankful to Prof. S.C. Roy – Member, NationalCommission of History of Science (INSA) and Editor-in-Chief, “Science and Culture” - Indian Science NewsAssociation, for commenting and correcting the earlyversion of this paper. Thanks are due to Prof. MichaelKomorek, Head of Research Group: Physics Didactic andHistory of Science, University of Oldenburg, Germany, forproviding research facilities. I am grateful to archivists of“Preußischer Kulturbesitz” Berlin and Bodleian LibraryOxford for providing with Born–Schrödinger and Krishnan-Peierls-Born-Raman correspondence respectively. Last butnot the least, I thank the editorial team and Prof. S.C.Lakhotia – Editor-in-Chief – “Proceedings of the IndianNational Science Academy” for sending me some of thepapers referred to in this paper.

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der mathematisch-physikalischen Klasse der KöniglichBayerischen Akademie der Wissenschaften zu München, 1912,pp. 303-322.

4. M. von Laue, Sitzungsberichte der mathematisch-physikalischen Klasse der Königlich Bayerischen Akademieder Wissenschaften zu München, 1912, pp. 363-373.

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S. C. SIRKAR, C. V. RAMAN AND DIFFUSE SPOTS IN LAUE ... Rajinder Singh.pdf · C.V. Raman in 1926; and did D.Sc. at the University of Calcutta. In 1940, C.V. Raman and his students