Photograph 49 is the Key to Understanding the History of Rosalind Franklin’s DNA Photograph 51

Sutton, Brian · SpringerLink

51 min read Original article ↗

Abstract

This essay, co-authored by a historian of science and an X-ray crystallographer, sheds new light on Rosalind Franklin’s Photograph 51. We refute the infamous claim that, unlike James Watson, Franklin failed to see the picture’s potential significance for interpreting the helical structure of DNA. Rather, Franklin decided to take Photograph 51 precisely because she knew that key parameters of DNA’s B form helix could be calculated from the resulting image. We show that she had in fact already made those calculations — on her earlier Photograph 49 — and she reused the same DNA sample for Photograph 51 to create a better-centered but otherwise identical diffraction image that would be suitable for publication. Thus Photograph 51 was not the result of an experiment in need of analysis, but was refined documentation for calculations that she had already performed on the earlier photograph. We argue that colleagues and later commentators did not merely overlook Franklin’s original reason for creating the strikingly clear and informative Photograph 51, they rhetorically erased her skill and judgment by describing it as though nature spoke for itself through the image — and to Watson, but not to Franklin.

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Introduction

Rosalind Franklin’s Photograph 51 (see Fig. 1) became famous because James Watson wrote that it spoke powerfully about the secret of life. “The instant I saw the picture,” he narrated in his controversial memoir The Double Helix, “my mouth fell open and my pulse began to race” (1968b, p. 167).Footnote 1 It was early February 1953 and Franklin’s estranged colleague Maurice Wilkins had shown Watson this X-ray diffraction image of DNA in a state known as the B form.Footnote 2 As Watson described it, he immediately recognized that the pattern on Photograph 51 “could arise only from a helical structure […] mere inspection […] gave several of the vital helical parameters” (1968b, pp. 168–169). Spurred on by seeing the image and learning of some measurements Franklin had taken of the B form diffraction pattern, Watson and Francis Crick began a fresh effort to build helical models of DNA and within a few weeks managed to produce their double helix.Footnote 3

While Watson’s book made Franklin’s Photograph 51 famous, his story gave the impression that she had not been able to recognize its significance the way he did. Consequently, many scientists, journalists, and biographers have sought to explain Franklin’s apparent neglect of a picture that, in retrospect, was so clearly suggestive of a helical molecule (Table 1).

Table 1 Key dates in the history of Photographs 49 and 51

Full size table

By consensus, what happened when Photograph 51 was taken in early May 1952 is that Franklin put the picture aside and did nothing with it, instead devoting months to studying the crystalline form of DNA known as the A form. In late February 1953, her notes show, she began to use Photograph 51 to understand the B structure. By then it was too late: she was still working when Watson and Crick solved the puzzle a few days later.

Several overlapping reasons have been given for Franklin’s apparent initial disregard and subsequent delay: she was only interested in the A form of DNA; she had only captured a B form pattern in Photograph 51 by accident, and as such considered it a distraction; she was resistant or even hostile to the suggestion that DNA was a helix. For Horace Judson, writing what remains the best-known journalistic account of Watson and Crick’s discovery, this added up to something like willful deafness on Franklin’s part. “The pattern shouted helix,” Judson lamented, but for nearly ten months she “turned her back on her own discovery of the B structure of DNA and her own best evidence that [it] was helical” (Judson 1979, p. 135).

We write here to contend that Photograph 51 shouted “helix” so clearly because Rosalind Franklin intended it to do so. She had already photographed the very same sample of DNA used for Photograph 51, and analyzing the prior diffraction pattern, Photograph 49 (Fig. 2), led her immediately to a number of significant conclusions about the dimensions of a helical DNA molecule. She then created Photograph 51 for the purpose of reproducing that valuable diffraction pattern in a better-composed image that would be suitable for publication. Whereas Watson and others have portrayed Photograph 51’s combination of visual excellence and theoretical significance as a kind of happy accident that Franklin failed to exploit, it was the desire to merge those qualities in a single exposure that had in fact driven her to take Photograph 51. By recapturing Franklin’s original motivation, we are in turn able to explain the subsequent actions which have been misinterpreted by her supporters and critics alike.

We will present our revisionist account first and then use it to reassess portrayals of Franklin. We begin with a short but detailed explanation of how photographs 49 and 51 were created around the beginning of May 1952 and how Photograph 51 came to serve its purpose as an image intended for circulation. We analyze the later emergence of claims that Franklin had ignored or misunderstood Photograph 51, and argue that these criticisms echoed longstanding tropes about the role of women in science and of photographs as scientific evidence.

Fig. 1

Rosalind Franklin’s personal copy of Photograph 51. On this glossy photographic print Franklin noted “NaDNA ‘Structure B’” upon the reverse (History of Molecular Biology Collection, Box 10, Folder 15, Science History Institute. Philadelphia)

The Significance of Photograph 49

The key to understanding why Franklin took Photograph 51 lies in her notes about a previous picture. It was the forty-ninth in a series of seventy-eight diffraction images she and her graduate student Raymond Gosling captured with a Philips micro-camera (see Fig. 2) at King’s College London in 1951 and 1952.Footnote 4 Months before taking Photograph 49, the pair had established the existence of two distinct structural forms of DNA, and they had begun to manipulate samples intentionally to create them. The A form possessed an almost crystalline structure and gave diffraction patterns with many spots, potentially offering a great deal of information for structural analysis (by calculation of Patterson maps).Footnote 5 DNA could be converted to the B form at high relative humidity, yielding a simpler diffraction pattern with too few spots for similar (Patterson) structure calculations. Franklin had discussed her discovery of the distinct A and B forms in a colloquium at King’s on 21 November 1951 and documented them in an annual report of 7 February 1952, but her results were not otherwise published.Footnote 6

Franklin’s annual report of February 1952 also laid out a research plan that she appears to have followed closely until she moved from King’s College to Birkbeck College in the spring of 1953. Her goals were twofold: (1) to determine what caused a given DNA sample to exhibit the A or the B form, and afterward, (2) to characterize both forms initially through Patterson analysis of the more complex but data-rich A pattern.Footnote 7

Photograph 49 was created two months later in the course of a lengthy series of experiments aimed at completing the first of these objectives. Franklin’s stated hope was that these experiments would also reveal the best techniques for capturing sharp DNA diffraction patterns. As hoped, it was during this period of systematically manipulating the humidity levels at which samples were stored and photographed that she and Gosling produced what they retrospectively considered their best ever A form pattern (Photograph 42 of early February 1952) as well as their best B form photographs in May.

Completed on the morning of 2nd May 1952, Photograph 49 showed the result of aiming an extremely fine X-ray beam for three days and nights at a fiber that had been pulled into a fine thread from a drop of gel-like concentrated DNA solution.Footnote 8 The beam emerged from a collimator at the front of the camera and met the sample fiber, which was mounted and held in place across the orifice by two drops of glue, immediately inside the camera, just 15 mm in front of the X-ray film that recorded the diffraction pattern (see Fig. 2). Because space within the camera was so tight, they employed an unusual technique to prevent the main (undiffracted) X-ray beam from overexposing the center of the film. Instead of blocking the main beam with a small circular piece of heavy metal such as lead between the specimen and the film, as was conventional in larger cameras, they punched a hole through the centers of all the stacked films and allowed the undiffracted beam to pass right through the films and out of the back of the camera, through a small fluorescent screen that facilitated camera alignment (the holes can be seen in the film and camera body shown in Fig. 3).Footnote 9 Franklin and Gosling controlled the relative humidity of the DNA sample throughout the days-long experiment by passing hydrogen gas that had been bubbled through an aqueous salt solution of defined composition and concentration into the body of the camera.Footnote 10

As with the trials that preceded Photograph 49, they would learn the result of the experiment by removing and developing a stack of two or three small, hand-cut pieces of film from where they were held inside the camera body during the exposure (see Fig. 3). Each of the duplicate (or triplicate) films would show an even smaller X-ray diffraction pattern about 2.5 centimeters in diameter. On this occasion, they had used two pieces of film marked in Franklin’s handwriting as 49A and 49B (see Fig. 4).Footnote 11

These Photograph 49 films showed an unprecedentedly sharp version of the diffraction pattern produced by DNA’s B form (Fig. 2). Franklin and Gosling accomplished this by using a sample that had become irreversibly locked into the high-humidity B structure, meaning that it could be mounted taut in the camera and photographed at the lower 75% humidity level that ordinarily produced an A form pattern.Footnote 12 The resulting fine definition made it possible to use the photograph for more precise analysis than any previous B image had allowed, and Franklin therefore gave it her prompt attention. This immediacy is evident from a separate series of notes that were headed “(49) 49B Rough measurements on projection,” dated 2 May 1952 — the very same day she and Gosling had developed the films.Footnote 13 These notebook pages began with measurements of the new diffraction pattern, which the pair enlarged by projecting it onto a piece of white cardboard, and Franklin’s notes progressed in short order to making general conclusions about the B structure of DNA. She noted that the molecule showed repeats occurring every 34 Å, meaning it was about 25% longer per repeating unit than the drier, more crystalline A form she had already begun to analyze.

From the day Photograph 49 was taken, Franklin interpreted the pattern as indicative of a helix.Footnote 14 Other evidence indicates that she already had a helical interpretation of the B form structure in mind, and now she calculated how many layers of purine and pyrimidine bases there must be “per turn of helix (if there is a helix).”Footnote 15 If the bases were spaced 3.4 Å apart, as she and other researchers believed, then her calculations suggested that there would be exactly ten nucleotide-base layers in each lengthwise repeat of the molecule. In her notes, she phrased the finding more generally: “there is an integral number (or single fractional number) of residues per [34 Å] turn.”Footnote 16 Later, in 1954, Watson and Crick acknowledged that they had built their double helix as a model of the B form with its 34 Å axial period containing ten base layers per turn, which, Watson and Crick crucially realized, were complementary base pairs rather than individual bases. It is not widely appreciated that these parameters were originally established in Franklin’s analysis of Photograph 49.Footnote 17

Fig. 2

Photograph 49. This glass-plate negative shows an identical diffraction pattern to that of Photograph 51, seen in Fig. 1, except that the pattern is cropped by poor alignment between the film holder and the X-ray beam; the upper 3.4 Å arc is almost entirely lost. Both exposures used the same DNA sample under the same conditions (KDBP 1/1/0868, King’s College London Archives). Courtesy King’s College London

Today Photograph 49 survives in its entirety only as a negative-image contact plate of film 49B held at the King’s College London archive (Fig. 2). The photograph is remarkable for two distinct reasons. First, it vividly captures the very same diffraction pattern known so well today from Photograph 51. Secondly, however, a portion of the famous pattern has been cut off. Through our examination of the camera Franklin and Gosling used in 1952, we can explain how this must have happened. The photographic films were held in place by a flat metal bracket whose edges were bent around a backing plate that the films rested against (Fig. 3). This holder has a slightly irregular circle of roughly 2.5 cm diameter cut out to allow the diffracted X-rays to hit the films, and the glass negative of 49B illustrates that this holder had become misaligned with the X-ray beam and the DNA sample. In consequence, the upper part of the pattern is cropped to such an extent that a large, arc-like region now familiar from Photograph 51 (Fig. 1) does not appear in the image. This missing arc, like its symmetrical counterpart which appears at the bottom of Photograph 49, is caused by the 3.4 Å spacing between each layer of nucleotide bases in the molecule.

As we have seen, this inadvertent cropping did not prevent Franklin from using Photograph 49 in her analysis and calculations. She had captured enough of the pattern to be able to discern that one of the 3.4 Å arcs was located on the tenth meridional layer line of the pattern and to understand the implications for quantifying the layers of bases stacked in a single 34 Å turn of the helical molecule. Photograph 49 was a sharp and usable image but, because of the equipment malfunction, it was poorly composed and thus less than ideal for public presentation.

Fig. 3

X-ray micro-camera and film. This recent picture illustrates how X-ray films were prepared for the Philips micro-camera (KDBP 6/4/7, King’s College London Archive) that was used to take photographs 49 and 51. From left to right: the front of the camera body, removed and viewed from the inside; a piece of X-ray film backing paper showing how films were cut to the appropriate size; the film holder (above) and a piece of developed X-ray film (below) showing that the region of the film exposed to X-rays was determined by the cut-out in the holder; the camera body back, containing the rectangular platform against which one or more small pieces of film were held in place by the film holder. The film and backing paper are surviving artefacts from Wilkins’ 1953 research with Herbert Wilson, which included replications of Franklin and Gosling’s work using different sources of DNA (K/PP178/2/8, Wilkins Papers). Photograph by Alistair Sponsel, July 2026

Franklin therefore decided to retake the photograph. On the evening of 2 May 1952 – still the same day she first saw Photograph 49 – she began the notebook entry for Photograph 51: she would use the same specimen from 49, the same X-ray setup, and the same 75% relative humidity within the body of the camera.Footnote 18 The only thing distinguishing this from being an exact repeat was, as she wrote, that Photograph 51 was taken “with [the] holder centered over [the] collimator so as to include both 3.4 [Angstrom] arcs.”Footnote 19

Photograph 49 had been a research image, the result of an experiment. Photograph 51 would be the exact opposite: a refined image taken after the fact to document that experiment’s particularly successful outcome.Footnote 20

This relationship between Photographs 49 and 51 emerges all the more clearly when Franklin’s notes about them are compared with earlier entries in her laboratory notebooks. She had by then established a note-taking routine well suited to the open-ended trials characteristic of Photographs 1–49, with two distinct parts for each entry. The first section, written before the photograph was taken, provided details of the experimental set-up, including the date and time when X-ray exposure commenced. Afterward, Franklin would record the date and time when she and Gosling ended the exposure and then complete a second section, for which she customarily left a few lines empty, giving a brief indication of how the experiment had turned out.

Initially, she wrote about Photograph 49 using her standard format. She first specified which DNA sample she was using, the relative humidity at which it was maintained, and the source of the X-rays. Three days later, she filled in the space below to report that this trial had produced a “V[ery] good ‘wet’ photo” (meaning a very good photo of the B form). However, she then turned to a fresh set of pages in the notebook and filled them with the analyses we discussed above. Headed with the very date the photograph had originally been developed, this passage of notes filled far more space in her laboratory notebooks than did the discussion of any single previous DNA diffraction pattern, indicating that she immediately found this version of the B pattern to be strikingly important.

The entry for Photograph 51 was unprecedented in a completely different way. This was the first instance in Franklin’s DNA laboratory notebooks where she was able to write down in advance what details the diffraction pattern would include (namely, both 3.4 Å arcs) and the first occasion when she specified that correcting the cropping of a previous photograph was the reason for taking a new one. As an understandable consequence, Franklin did not bother to fill the lines at the end of entry 51 where she would normally have described the result of the photograph. Indeed, the empty space stands out starkly on a pair of pages otherwise densely filled with the initial conditions and the results of the surrounding experiments. As discussed below, later commentators have misinterpreted this omission as the act of a person who had just conducted a potentially crucial experiment, but who didn’t appreciate its significance. Rather, as we have shown, Photograph 51 was not an experiment at all in the sense that trials 1 to 50 had been. It was, in fact, the product of Franklin’s decision to invest four days of X-ray time into a known outcome. The investment made sense precisely because she valued a high-quality photograph of the helical B form diffraction pattern.

Franklin and Gosling did not immediately publish Photograph 51. Later commentators, armed with the knowledge that it would be less than a year before Watson and Crick built their double helix as a physical model of the very B form structure Franklin and Gosling discovered and characterized, have criticized Franklin for directing much of their effort during the rest of 1952 to analyzing the A form. However, what critics describe as Franklin’s discovery — and subsequent apparent neglect — of evidence for the crucial B form structure of DNA looked different from her perspective and in the context of her broader research objectives. Franklin’s stated objectives, as we have seen, were to understand the relationship between and interconversion of the two forms of DNA. Photographs 49 and 51, and her analysis of the former, which revealed the key parameters of a helical structure, represented an important and successfully achieved milestone. It is only with hindsight that we view the B form structure as the only important goal, and the structure of DNA. DNA clearly had more than one structure and Franklin wanted to solve both of them.

Fig. 4

The handwriting on individual films of photographs 49 and 51 (KDBP 1/1/0867–868, King’s College London Archives) compared with entries in Franklin’s notebooks (FRKN 1/1, Franklin Papers; reproduced with the kind permission of the Trustees of the Franklin Archive)

By completing Photograph 51, Franklin now had good images in hand of both the A form and the B form. From here, she turned to the second major objective of her established research plan: detailed structural analysis beginning with the crystalline A form, whose pattern offered more data for analysis than the paracrystalline B form. The results of several months’ work led her to conclude that this crystalline structure was likely a double-chained molecule, and in February 1953 she turned back to Photographs 49 and 51 to assess whether the B structure in turn showed “evidence for [a] 2-chain […] helix.”Footnote 21 That the B form photographs indicated a helical structure however, was not in doubt, as indicated by her notebooks. By the end of February, as she was leaving King’s College for a position at Birkbeck College, she and Gosling had drafted three papers, two of which would contain Photograph 51 when they were published later that year.Footnote 22 Meanwhile, since Gosling was to remain at King’s to finish his PhD under Wilkins’ supervision, Franklin directed him to give Wilkins the diffraction photograph that Wilkins in turn showed Watson.Footnote 23

For all the investment Franklin originally made to capture a publication-worthy version of the B pattern, when it came time to publish Photograph 51 she took yet another step to refine the image. In early March 1953, she turned over film 51C to be duplicated onto a durable glass slide negative that could, in turn, be used to produce positive photographic prints for submission.Footnote 24 The slide, which survives and is numbered 867 in the biophysics unit’s indexing system, became the basis for published reproductions.Footnote 25 This is evident because published images of Photograph 51 show the diffraction pattern centered within a circular border even more precisely than it had been when the pattern was originally developed on film. The perfected cropping was achieved by placing masking tape on the glass plate itself (see Fig. 5). The figures of Photograph 51 in both of Franklin and Gosling’s 1953 publications (1953a and 1953b) that included it show the ultra-refined cropping from the glass plate.

Fig. 5

A composite image showing how Photograph 51 was further cropped for publication. Left: a hitherto unpublished print of Photograph 51 showing that the circular region of exposed film had been larger than necessary to succeed in capturing the full diffraction pattern (HMBC Box 10, Folder 15). Center: the glass plate negative of film 51C with red masking tape used to create a new, smaller circular margin centered precisely on the diffraction pattern, which left a penumbra that can still be seen faintly through the tape in the lower-right quadrant of the slide (KDBP 1/1/0867). Right: Photograph 51 as it appeared in publications, shown here in the 25 April 1953 issue of Nature (Franklin and Gosling, 1953a)

Rethinking Rosalind Franklin’s Reputation in Light of Photograph 49

The myth that Franklin had failed to see value in Photograph 51 arose as a consequence of Watson’s 1968 memoir The Double Helix. The book appeared fifteen years after the events in question, ten years after Franklin’s tragically early death from ovarian cancer, and six years after Watson, Crick, and Wilkins shared the Nobel Prize for their studies of DNA. The book caricatured her as both a machine-like researcher and as a woman with emotions she could not control. In Watson’s telling, her “years of careful, unemotional crystallographic training” meant that she was producing sharper diffraction photographs and consequently more detailed measurements than anyone else (Watson 1968b, p. 69). However, she would erupt into defensive outbursts at any attempt to help her interpret these proprietary data, making life an “emotional hell” for her colleague Maurice Wilkins (Watson 1968b, p. 167). Indeed, Wilkins supposedly showed Photograph 51 to Watson in a moment of solidarity when Watson had invoked Franklin’s “hot anger” by suggesting to her face that “she was incompetent in interpreting X-ray pictures” and needed to “learn some theory” (1968b, p. 166).

Watson’s harsh portrayal of Franklin inspired many reactions, one of which came from her friend and former Birkbeck colleague Aaron Klug. Klug had inherited many of Franklin’s King’s College research records, and he now sought to understand what she had known about DNA, and when. After finding her 1951–1953 laboratory notebooks, he studied them carefully and circulated annotated photocopies for discussion with Wilkins and others (including historian Robert Olby, who was then working closely with Crick while doing research for a planned book). This flurry of activity in 1968 revealed that the well-known published B form pattern had been called Photograph 51 in her notebook and that it had been taken at the beginning of May 1952.Footnote 26 Wilkins reacted by declaring it a “real tragedy” that, in keeping Photograph 51 to herself for the rest of year, Franklin had allowed Watson and Crick to race ahead of the King’s group. “I looked at that B form picture,” Wilkins said in reference to receiving it from Gosling in January 1953, “and there it was, you can see the helix right there on the picture, but she refused point-blank to see it.”Footnote 27

Fig. 6

Rosalind Franklin in a 1950 photograph by the crystallographer Vittorio Luzzati (History of Molecular Biology Collection, Box 10, Folder 14. Science History Institute. Philadelphia)

Sentiments like Watson’s and Wilkins’ had a profound impact on the historical treatment of Franklin’s work. The question became, how did Franklin fail to discover the double helix while she possessed the photograph that supposedly had spurred Watson and Crick’s success?Footnote 28 For example, consider how the journalist-historian Horace Judson wrote about her in his celebrated 1979 book The Eighth Day of Creation, which was based on extensive interviews with all the participants except the late Franklin herself. Knowing with hindsight that Photograph 51 was the B picture she would later publish, he used it as a narrative device to portray a singular moment when Franklin decisively failed. “The pattern shouted helix,” Judson wrote, and it even “whisper[ed]” the other details of the B form structure. Although he mentioned the analysis she had performed on Photograph 49, his characterization was that Franklin merely “thought briefly and tentatively about No. 49” and “[t]here she stopped.” By underestimating the novelty and significance of these calculations and, more importantly, by misjudging why she had chosen to take Photograph 51, Judson interpreted the lack of notes about the retaken photograph as a sign that she had “turned her back on her own discovery of the B structure” (Judson 1979, p. 135). We do not believe that Franklin ever turned her back on the B form. Deciding to take Photograph 51 was not a moment of failure, but a mark of her future commitment.

We have seen that Watson portrayed himself as immediately hearing the helix’s metaphorical shout from Photograph 51. He went on to insist throughout his life that Franklin had not been a sufficiently good scientist to see in Photograph 51 the truths that he had instantly recognized in the B form pattern. In a 2008 interview, for example, he said Franklin “clearly wasn’t interested in theory very much” and had neglected to pursue the B form even though it “was the perfect helical thing.”Footnote 29

These phrasings portrayed Photograph 51’s simple, sharp B form diffraction pattern as a natural object rather than a human-produced research product — as though it had occurred spontaneously under Franklin’s watch rather than being generated and photographed on purpose. In Judson’s telling, the DNA molecule “whispered” and “shouted” directly to those who saw the picture, rhetorically erasing the role Franklin played in revealing nature’s secrets (1979, p. 135). We have seen that Wilkins went even further, speaking as though Franklin had been concealing nature’s secrets by possessing Photograph 51.

The conceit that nature could speak directly to Watson through Photograph 51 echoed language that dates back to the earliest use of cameras by scientists. Advocates of the new technology claimed that photography, by reproducing natural objects mechanically and therefore without human bias, supposedly allowed nature to speak for itself. As historians Lorraine Daston and Peter Galison have shown, this combination of rhetoric and technology stemmed from the 19th-century craze for achieving “objectivity” in scientific research. Although technique and even creativity were actually required to make nature (seemingly) imprint itself on a photographic plate, the objective scientific photographer’s goal was to render this work invisible (Daston and Galison 2007, p. 133). One of Franklin’s contemporaries, the great crystallographer J. D. Bernal, alluded to this process shortly after her death. Having pointed out that Franklin captured “among the most beautiful X-ray photographs of any substance ever taken,” Bernal remarked on the “skill” that had allowed her to make those photos appear to be “effortless.”Footnote 30

However, merely highlighting Franklin’s technical acumen risks damning her with faint praise for her contributions to the discovery of the double helix. It is one thing to possess the skill necessary to let a molecule seemingly speak for itself through a beautifully clear photograph, but it is another thing to be able to discern which specimen must be heard in order to solve an important scientific puzzle. To flip Watson’s deprecating remark on its head, this does require an interest in theory. It requires knowledge and judgment. In Franklin’s case, not only had she recognized the conceptual value of the B form diffraction pattern captured in Photograph 49, but she had also devised the original series of humidity experiments that revealed the B form’s existence and enabled her to capture it so clearly.

Franklin was an accomplished, creative, and self-directed researcher, but Watson’s Double Helix cast her in the role of a technical plodder, unimaginatively toiling over samples, laboratory equipment, measurements, and calculations.Footnote 31 Later efforts to praise her as a skilled crystallographer (but by implication nothing more), often reinforce a long tradition of women’s scientific activities being treated as rote work.Footnote 32 Recently, as Franklin’s public profile has risen considerably, her role in the hands-on work of crystallography has, in turn, been called into question. In what we consider to be an oversimplified description of a multi-day, multi-instrument collaborative undertaking, Gosling is now regularly credited as the sole individual who took Photograph 51.Footnote 33

Evidence from throughout Franklin and Gosling’s notes illustrates her leadership of, and thorough involvement in, both the intellectual and technical aspects of this collaborative research. Her handwriting on the films of photographs 49 and 51 (see Fig. 4) indicates that she was present when the films were loaded into the camera, but both Franklin and Gosling were likely aided by other women working alongside the King’s College biophysicists. Freda Ticehurst was the unit’s scientific photographer and manager of the dark room. She, in turn, had assistance from the likes of Lucille Heller, who volunteered in the biophysics unit in 1950–1951 and recalled “I remember helping Gosling set things up, and I think I helped sometimes with taking the X-rays, and I helped Freda Ticehurst, the lab photographer, develop some of the images.”Footnote 34 Gosling himself recalled the assistance and collaboration he and Franklin received from one of the biophysics unit’s workshop technicians, Len Pitches, who modified and even built cameras and other apparatus to their specifications.Footnote 35

Our case study of the relationship between photographs 49 and 51 provides only a glimpse at the full arc of Franklin’s activities as a DNA researcher.Footnote 36 However, even within this short paper we have witnessed her pursuing a full spectrum of scientific activities: designing a highly consequential series of experiments, tapping the skills of her student and technical staff while working alongside them in the X-ray room, accumulating data and carrying out careful measurements, perceiving the value of her results, and also showing a persistent intention about how to make the result we focused on here — the B diffraction pattern — appear in the most arresting possible form when it was published. She created Photograph 51 to serve as evidence of a helical DNA structure, of her laboratory's technical virtuosity, and of her own scientific judgment.Footnote 37

Data Availability

No datasets were generated or analysed during the current study.

Notes

  1. In the main text, Watson did not specify exactly which of Franklin’s photographs he had been shown by her colleague Maurice Wilkins. However, Photograph 51 is the one he used to illustrate this episode in the first edition of The Double Helix (Watson 1968b, p. 168).

  2. In her notebooks and in an interim report dated 7 February 1952, Franklin used the terms “crystalline” and “wet” to describe the two structures that she and her PhD student Raymond Gosling had successfully characterized (FRKN 1/1 and FRKN 4/3 respectively in Papers of Rosalind Franklin, Churchill Archives Centre, Cambridge; hereafter, Franklin Papers). These structures were called A and B respectively in the first publication she drafted with Gosling (Franklin and Gosling 1953b). As we discuss below, it was Franklin herself who had characterized these two forms as distinct structures. For ease of understanding, we will refer to the structures as A and B throughout the paper.

  3. Many later commentators, acknowledging the significance of Photograph 51 to Watson and Crick’s discovery, have declared it to be among the most important photographs ever taken. (See, for example, assertions of Photograph 51’s historic significance in Walsh 2012 and Babaian 2024). Its appearance in compendia of influential photographs such as LIFE 100 Photographs: The Most Important Pictures of All Time and the Stories Behind Them (Editors of LIFE Magazine 2021) implies the same. Photograph 51 has also been featured on the British fifty-pence coin minted in Franklin’s honor and it was the namesake of a prizewinning play in London’s West End (Ziegler 2015).

  4. FRKN 1/1, Franklin Papers. The notebooks have been made available online at https://wellcomecollection.org/works/uus54sbp. Note that Franklin and Gosling also took photographs with other apparatus and numbered them in separate series.

  5. Detailed discussions of the work mentioned here are available in Klug (1968), Olby (1994 [1974]), Elkin (2003). Patterson maps, calculated from the intensities and positions of the diffraction spots alone, can reveal prominent inter-atomic distances, such as between phosphate groups, from which structures may be deduced.

  6. Franklin’s notes for her November 1952 colloquium are in FRKN 3/2, Franklin Papers. The annual report is Rosalind Franklin, “Interim Annual Report” dated 7 February 1952. FRKN 4/3, Franklin Papers.

  7. She wrote, “It is proposed to attempt a quantitative interpretation of the [A form] fibre diagram (which shows a high degree of crystallinity in the DNA fibres) by means of Patterson functions. […] Before embarking on these calculations it seemed desirable to ascertain that the photographs used were [i.e., would be] the best which could be obtained.” She continued by describing the “preliminary results” of what were then ongoing efforts to pursue a “systematic search for the best conditions, especially with respect to relative humidity.”

  8. The following paragraph is based on specific information about the Photograph 49 experiment from Franklin’s 1952 notebook (FRKN 1/1, Franklin Papers) and on general information about the experimental set-up that we gleaned from studying the Philips micro-camera itself and from Raymond Gosling’s 1954 PhD thesis (KDBP 6/4/7 and KDBP/5/1 respectively, King’s College London Archive).

  9. In shedding light on this unusual technique of allowing the main part of the X-ray beam to pass through the entire camera apparatus, we hereby offer a detailed context for the concerns regarding Franklin’s radiation exposure that some of her colleagues later shared in interviews for Maddox’s biography (Maddox 2002, p. 144).

  10. Wilkins had originally suggested to Gosling the idea of filling the camera body with hydrogen gas to prevent unwanted scattering of the X-ray beam by the larger molecules in air. It was Franklin’s key contribution to control and modify the humidity of the hydrogen gas, and thus the DNA sample during the experiment, by bubbling the hydrogen through various salt solutions before it entered the camera.

  11. Franklin’s notebook entry for Photograph 49 specifies “2 films” (FRKN 1/1, Franklin Papers). The surviving version of Photograph 49 comes from film 49B (see Fig. 2). We infer that the other film would have been marked 49 A.

  12. We disagree with suggestions by Maddox (2002) and Cobb (2025, p. 85) that Franklin did not intend or expect Photograph 51 to exhibit a B form pattern. “Sometimes during exposure,” Maddox wrote, “the [DNA] fibre would change from the crystalline A form to the paracrystalline B form. Once this happened so abruptly that the fibre fell off the holder. The photograph taken between 1 and 2 May […] was the clearest picture ever taken of the B form of DNA […] Rosalind put it aside to return […] to the puzzle of the A form” (Maddox 2002, pp. 177–178). The circumstance Maddox described, of extremely hydrated DNA samples loosening in the specimen holder as a result of the structural shift from A to B, had indeed occurred with some of Franklin’s earlier experiments; for example, she had noted a “series” of trials in March and April 1952 “in which trial short-exposure films were generally good and [the] specimen subsequently went non-crystalline during long exposure” (note headed “March-April 1952” on the first inside page of Franklin’s 1952 notebook, FRKN 1/1, Franklin Papers). However, in the same note Franklin also reported the conclusion that specimens which began to give “non-crystalline” B form patterns at 75% relative humidity (which ordinarily produced the crystalline A form) were “never re-converted to crystalline.” It was just such a locked-in B form specimen, photographed at 75% RH, that she subsequently used to produce photographs 49 and 51. Indeed, Franklin and Gosling used Photograph 51 in one of their publications specifically to illustrate the phenomenon of “a fibre which had passed irreversibly to structure B” and which produced excellent diffraction images precisely because it was no longer susceptible to “buckling of the fibre in the wet state, and consequent deterioration of the quality of the photograph” (1953b, pp. 674–675). By tracing this particular DNA sample’s provenance back through Franklin’s notes, we can tell that it had been locked into the B form for several weeks. Her entries for photographs 49 and 51 indicate that both were taken of a “specimen […] which gave [a] good ‘wet’ photo” when previously used in the lower-humidity photograph T0 on 18 April (this had been the first of a separately numbered “T” series of pictures she and Gosling had taken using a custom-built tilting camera stand). In the entry for Photograph T0, in turn, Franklin said the sample was “previously Xtalline [crystalline, meaning the A form], now gives ‘wet’ diagram [i.e., B form]” (entries for photographs T0, 49, and 51, Franklin’s 1952 notebook, FRKN 1/1, Franklin Papers).

  13. Pages headed “(49) 49B”, Franklin’s 1952 notebook (FRKN 1/1, Franklin Papers). This notebook entry is reproduced as Fig. 21 in Klug (2004).

  14. We emphasize this point only to contradict claims (discussed below) that Franklin had not recognized Photograph 51 as evidence of a helical molecule. That such a diffraction pattern was suggestive of a helical molecule had been worked out by her colleague Alec Stokes at King’s (unpublished), and by Crick and others in Cambridge (published as Cochran, Crick, and Vand 1952).

  15. Pages headed “(49) 49B,” Franklin’s 1952 notebook (FRKN 1/1, Franklin Papers). Franklin had declared three months earlier, in her annual report, that her studies of the A form “suggest a helical structure (which must be very closely packed) containing probably 2, 3, or 4 co-axial nucleic acid chains per helical unit.” In briefer remarks about the B form in the same report, she mentioned the “helix in the wet state” while reporting the DNA molecule lengthened to an undetermined degree during the crystalline-to-wet (A to B) transition (“Interim Annual Report” dated 7 February 1952; FRKN 4/3, Franklin Papers).

  16. Thanks to the work of William Astbury and Florence Bell in the late 1930s, it was considered likely that 3.4 Å represented the spacing between layers of the nitrogenous bases stacked perpendicular to the long axis of the molecule. See Astbury and Bell (1938). For discussion of their work, see Kersten Hall (2014).

  17. We believe that other commentators, for example Cobb and Comfort (2023), are mistaken in implying that Wilkins had independently and/or previously established the 34 Å axial repeat for the B form. In fact, Wilkins made several notes in the 1970s suggesting that he was interested in working out when Franklin had managed to do it. For example, on a copy of Franklin’s 7 February 1952 interim report, he wrote “N.B. no mention of 34 Å period[.] I had pattern by then & it looks as tho’ none of us bothered to measure it!” (Wilkins, Maurice Hugh Frederick [1916–2004], King’s College London Archives (hereafter, Wilkins Papers) K/PP178/5/3; see also his efforts to remember when she had done it on pp. 3 and 13 of his reminiscence dated 17 September 1976 in K/PP178/5/27/1). By the time Wilkins told Watson details of the B form in early 1953, he would have learned about the 34 Å period from Franklin and Gosling’s 3 September 1952 contribution to their unit’s annual report to the biophysics committee of the Medical Research Council. In his various recollections, Watson himself later indicated that he learned details of Franklin’s measurements by viewing his colleague Max Perutz’s copy of that MRC committee report, as well as from Wilkins by word of mouth.

  18. The intervening Photograph 50, taken during the day on 2 May 1952, was a very brief exposure assessing the condition of a freshly prepared DNA sample that was then placed into a desiccator (FRKN 1/1, Franklin Papers).

  19. Entry 51 in Franklin’s 1952 notebook (FRKN 1/1, Franklin Papers).

  20. We are not the first analysts to discuss Franklin’s forty-ninth photograph, but we believe our formulation of its significance in relation to Photograph 51 is original. Aaron Klug (1968, p. 810) alluded to the existence of Photograph 49 by describing the image published in Franklin and Gosling’s Nature paper (i.e., Photograph 51) as one of multiple “photographs of exceptional quality [showing…] in a direct manner that DNA in the B form is a helix with an axial repeat of 34 Å and an axial spacing between nucleotides of 3.4 Å.” He continued, “The model building by [Watson and Crick…] was carried out to fit these parameters.” Robert Olby (1994 [1974], p. 369) also did not explicitly name Photograph 49, but he quoted Franklin’s 49th notebook entry (“V[ery] good ‘wet’ photo”) and speculated that this picture was the one Wilkins later showed Watson. On the following page, he quoted the notebook passage describing Franklin’s discovery of the 34 Å axial repeat but did not specify that it was accomplished using Photograph 49. Judson (1979, p. 135) did specify that the “good ‘wet’ photo” entry was a description of Photograph 49 and he noted that Photograph 51 was “set up […] with the film holder more perfectly centered on the X-ray source.” As we discuss in the main text below, however, he then shifted to asserting what he thought Franklin should have realized about these two images. That passage drew from (and, in the process, conflated) Franklin’s May 1952 analyses of Photograph 49 and her February 1953 analyses of Photograph 51. We also note that a recent post on the website of Jessica Mills Davies, the author of a novel based on Franklin’s life, is illustrated with two versions of Photograph 49, namely the negative we included above (Fig. 2) and a positive-image print that Gosling used in his 1954 thesis. See Mills (2024) and Jessica Mills Davies. 16 January 2026. “Photograph 49: The X-ray Watson did not see,” (https://www.jessiemillsauthor.com/journalism/photo-49-the-x-ray-watson-did-not-see, accessed 28 May 2026). Although we find many of Mills Davies’ specific claims about the photograph to be inconsistent with our understanding of Franklin’s work, we believe she is the first person to highlight publicly its appearance in Gosling’s thesis and to note the inaccuracy of his accompanying caption which mistakenly says it was exposed for the same duration as Photograph 51. Klug himself had noted this with some confusion inside his copy of Gosling’s 1954 PhD thesis, which he had inherited from Franklin and which is now in SHI HMBC, Box 14, Folder 1, notes on plates 4 and 10 of Chap. 4. As we show below, the error was originally made in the caption for Fig. 5 of the earlier publication by Franklin and Gosling (1953b, plate 10, inserted between pp. 674 and 675).

  21. Notebook entry for 10 February 1953 (FRKN 1/1, Franklin Papers).

  22. The paper drafted second but eventually published first was the expedited paper on the B form that appeared alongside Watson and Crick’s double helix paper on 25 April (Franklin and Gosling 1953a). The first paper to be drafted, about the relationship between the A and B forms, had already been submitted on March 6 but did not appear until the summer (Franklin and Gosling 1953b). Photograph 51 appeared in the latter paper as Fig. 4. It was accompanied by an extreme-closeup detail of the center of Photograph 49, as Fig. 5, to illustrate part of the diffraction pattern (an equatorial doublet) that was not entirely visible outside the central pinhole of the Photograph 51 film. With respect to the beam and the pinhole, Photograph 49 was slightly better aligned (both figures and their captions were printed on plate 10, inserted between pp. 674 and 675). The caption of Fig. 5 mis-stated the exposure time of Photograph 49 as 62 h, an error that Gosling carried forward to his 1954 PhD thesis (SHI HMBC, Box 14, Folder 1, notes on plates 4 and 10 of Chap. 4).

  23. In practice, Gosling continued working with Franklin while she was at Birkbeck. Their final co-authored DNA paper appeared in 1955.

  24. The King’s College biophysics unit maintained index books of quarter-plate slides produced for researchers (KDBP 2/1, King’s College London Archive). The first book in this series records that in March 1953 “Dr Franklin” ordered several plates including those duplicating films 51C and 49B (plates 867 and 868 respectively).

  25. There are several ways we can be sure that reproductions came from slide 867. For example, Franklin’s own copy of the image (see Fig. 1), has “867” written in pencil on the back of the print (along with her annotation in pen). More significantly, all published versions show the doubly refined cropping achieved by the placement of masking tape on glass plate itself (see Fig. 5). Presumably there must have been some prints made from the original film (as would have been the case for the print Wilkins showed Watson in early February 1953 nearly a month before plate 867 was made). The only print we are aware of that shows the original cropping from film 51C is the previously unremarked large-format print we have reproduced on the left of Fig. 5 (HMBC Box 10, Folder 15). This object was in Gosling’s possession as of the 1990s. In the same collection is a 4 inch x 5 inch (10.2 cm x 12.7 cm) acetate slide showing the patterns from photographs 42 and 51, i.e., Franklin and Gosling’s best A and B patterns, side by side and featuring the original cropping for Photograph 51 (HMBC Box 10, Folder 16). We are still working to solve the puzzle of when this slide was created and what it may have been used for.

  26. Klug wrote to Olby on 3 September 1968, “[b]efore leaving for holiday a few weeks ago, I discovered Rosalind Franklin’s missing notebooks for the years 1951 and 1952. This enables one to date all the photographs. […] Would you like to come and see them?” (HMBC Box 13, Folder 23).

  27. Maurice Wilkins 1970 interview with Anne Sayre for her book Rosalind Franklin and DNA, as quoted by Sayre (1975, p. 128). In the BBC film Life Story (1987), which was made in consultation with Wilkins, he is depicted as showing Watson a large print of Photograph 51 while telling him that its pattern is obviously representative of a helical structure. (Wilkins’ extensive files related to the production are in K/PP178/5/27, Wilkins Papers.)

  28. Many efforts to understand the nature of Franklin’s failure focus on her supposedly anti-helical views. Watson used the phrase several times in The Double Helix, attributing it to Wilkins. He wrote, “Maurice had told me the nature of her so-called antihelical results,” and described “her self-made antihelical trap” (Watson 1968b, pp. 165–166). As Robert Olby (1994 [1974], p. 371) has pointed out, Wilkins seems to have misjudged the significance of her anti-helical data (which he had not seen) and/or the sincerity of her antihelical views (1994 [1974], p. 371). We largely agree with the explanations given by Klug (1968) and Olby (1994 [1974], pp. 370–376) for why Franklin felt, from late 1951 to early 1953, that there was a lack of evidence to conclude that the A form was helical.

  29. James Watson interview with Martin Raff and Walter Gratzer, recorded November 2008 and October 2009, section “Rosalind Franklin’s rapid acceptance of the double helix,” Web of Stories, 18 June 2010, https://www.webofstories.com/play/james.watson/32 (accessed 29 May 2026).

  30. Bernal wrote two obituaries of Franklin, both of which are quoted here. He called her images “among the most beautiful X-ray photographs” in memorializing her for Nature (Bernal 1958), and he discussed her “apparently effortless skill” in The Times (J.D. Bernal, “Dr. Rosalind Franklin: A life dedicated to science,” The Times (London), April 19, 1958, p. 3).

  31. Amplifying earlier observations by Maddox (2002, pp. 311–328), Angela Creager and Gregory Morgan (2008, p. 270) have argued that “the image of Franklin as meticulous and unimaginative […] was offered by Crick as well as by Watson, and the depiction works to excuse both of them for using her data by suggesting that she did not seem to know how to interpret it herself.”

  32. The most vivid illustration of this phenomenon appears in an essay Judson appended to the 1996 edition of his book in response to those who had adopted Franklin as “an emblem for the condition of women in science” and given her what he considered undeserved credit for Watson and Crick’s intellectual breakthrough. Franklin had been “patient, dextrous [sic], untiring,” he argued, which meant that she had been “poignantly unlucky” to lack a collaborator like Watson. “His scientific imagination [was] intensely visual,” Judson wrote, so that Watson “understood instantly facts [about Photograph 51] that Franklin had only [later] figured out” (Judson 1996, pp. 627–628). This points beyond the more general phenomenon of women receiving less attention and acclaim than men for similar scientific achievements, which historian Margaret Rossiter termed the “Matilda Effect” (Rossiter 1993). Regarding the specific tendency we noted, Naomi Oreskes has written, “the invisibility of women’s contributions is enmeshed with the question of why some kinds of scientific work are more valued and honored than others” (Oreskes 1996, p. 87). Because of sexual segregation in scientific and military institutions, many women were formally limited to holding technical or computational positions that were considered lower status, even if their activities transcended the nominal limits of their roles. Women in these roles became emblematic of “routine” scientific labor, making them all but ineligible to receive recognition according to the “rhetoric of [scientific] heroism in the public sphere” (Oreskes 1996, p. 113). Pnina Abir-Am has made a similar but nevertheless distinct argument regarding creative contributions to the Nobel-prizewinning discovery of RNA splicing by the electron microscopist Louise Chow, whose work she says was not recognized for its novelty and significance by other participants who were less experienced in microscopy (Abir-Am 2020).

  33. As one illustration of this trend’s recent intensification, compare passages from a 2023 coauthored paper by Matthew Cobb and Nathaniel Comfort with Cobb’s 2025 biography of Crick. The former describes Photograph 51 as “a particularly clear image of the B form, taken […] by Franklin and her graduate student Raymond Gosling” (Cobb and Comfort 2023, p. 658). The latter describes it as “an X-ray diffraction image of the B form supposedly taken by Franklin (in fact by Gosling)” (Cobb 2025, p. 85). The trend seems to date from statements by and about Gosling around the time of the sixtieth anniversary of the double helix (see Smith 2019; Attar 2013, 2023). We also note with good humor that the opening sentence of the current Wikipedia entry for Photograph 51, which says that the picture was “taken by Rosalind Franklin’s PhD student Raymond Gosling,” incongruously cites as its source an article by one of the present authors (Brian Sutton) that says the photograph was taken by Franklin and Gosling (https://en.wikipedia.org/w/index.php?title=Photo_51&oldid=1364555388; accessed 22 July 2026).

  34. In an obituary for Ticehurst (then known by her married name of Freda Collier) in the Guardian, her nephew claimed that she had taken Photograph 51. Our general impression from all available evidence is more consistent with Heller’s recollection, namely that Ticehurst was likely involved in developing films after the experiments were complete (and creating duplicates on glass slides and in photographic prints). Heller’s recollections are from a July 2022 interview with Judy Masterson published on the website of Rosalind Franklin University in Chicago (https://www.rosalindfranklin.edu/helix/winter-2023/being-there/). The Ticehurst obituary is Thirlwall, A. P. 2013. “Freda [Ticehurst] Collier Obituary.” The Guardian, January 21 (https://www.theguardian.com/science/2013/jan/21/freda-collier-obituary).

  35. Raymond Gosling interview with Anne Sayre, 18 May 1970. Anne Sayre Collection of Rosalind Franklin Materials, Box 4, Folder 2, p. 15; Archive of the American Society for Microbiology, Baltimore, Maryland.

  36. Franklin’s well-roundedness as a virus researcher — specifically the combination of leadership, crystallographic skill, and theoretical intuition she displayed in her 1953–1958 studies of Tobacco mosaic virus structure — has been well documented by Angela Creager and Gregory Morgan (2008).

  37. Sociologist of science Michael Lynch highlighted the distinction between photographs taken for “use” and photographs subsequently taken to be published as “evidence,” noting that several microscopists had told him they would avoid publishing blemished images that they had actually studied if they could instead illustrate their research with a visually “perfect” picture. Lynch concluded that "the documentary use of a photograph in a [publication] differs considerably from that of a photograph used by lab members [in the course of doing the original research].” Well-composed and unblemished photos for publication would not only illustrate research findings clearly but also serve as “exhibits of a lab’s practical competence” (Lynch 1985, pp. 94–96). We are grateful to Simon Schaffer for drawing our attention to this passage.

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Acknowledgments

We are extremely grateful to the archivists, librarians, and/or digital-collections staff of the Center for the History of Microbiology Archive in Baltimore, Churchill Archives Centre in Cambridge, King’s College London Archives (with special thanks for introducing us to each other), and the Science History Institute in Philadelphia (SHI) for making our research possible, and also to SHI colleagues/friends for supporting our collaboration. We are also grateful to our JHB editors, Nic Rasmussen and Betty Smocovitis, for their energy, advice and innumerable contributions to improving the paper; to two JHB referees for their helpful comments on the original manuscript; and to the following individuals for valuable conversations and/or comments on written drafts: Geoff Browell, Matthew Cobb, Nathaniel Comfort, Angela Creager, Michelle DiMeo, Hannah Grunwald, Judith Kaplan, Madison Renner, Lukas Rieppel, Simon Schaffer, Valerie Sponsel, Hallam Stevens, and Andrew Warwick.

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This research was not supported by any external funding.

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  1. Science History Institute, Philadelphia, USA

    Alistair Sponsel

  2. King’s College London, London, UK

    Brian Sutton

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  1. Alistair Sponsel
  2. Brian Sutton

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AS and BS conducted all of the research, much of it while working side by side on archival materials, and developed the argument together. AS wrote the first draft and prepared the figures. AS and BS contributed equally to all subsequent writing and revision of the manuscript.

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Correspondence to Alistair Sponsel.

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Sponsel, A., Sutton, B. Photograph 49 is the Key to Understanding the History of Rosalind Franklin’s DNA Photograph 51. J Hist Biol (2026). https://doi.org/10.1007/s10739-026-09866-7

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