Rosalind Franklin’s camera was a simple device made of brass, only a little larger than a fist. Small pieces of X-ray film were placed inside it. Over a narrow opening at the front, Franklin and her student Raymond Gosling attached a thin fibre that had been pulled from a solution of DNA. To make each image, they directed a fine beam of X-rays into that opening for hours, sometimes for days. In the spring of 1952, at King’s College London, one of these exposures gave them the clearest diffraction pattern they had yet obtained. The image was not perfect, however. The film holder inside the camera had slipped, so the pattern was not in the centre and one edge of it was missing.
This image was known as Photograph 49. On the same day that she saw it, Franklin began a new exposure of the same sample. That second image became Photograph 51, which is the most famous picture in the history of molecular biology. For more than fifty years, the usual version of events has said that Franklin did not understand what her own picture revealed. A paper published on 5 October 2026 in the Journal of the History of Biology argues that the reverse is true. Its argument is based on the earlier photograph, the one that had been forgotten.
The usual version comes mostly from James Watson. According to his account, Maurice Wilkins showed him one of Franklin’s DNA photographs at King’s in 1953, and Watson suddenly understood something important. “The instant I saw the picture my mouth fell open and my pulse began to race,” he wrote. In The Double Helix, the autobiography he published in 1968, he presented the photograph as the moment when everything became clear to him: “The black cross of reflections which dominated the picture could only arise from a helical structure.”
Other writers repeated the claim that Franklin had seen the same pattern without realising what it meant. Horace Judson wrote what is still the best-known account of the discovery by a journalist. In 1979 he wrote that “The pattern shouted helix,” but that for almost ten months Franklin “turned her back on her own discovery of the B structure of DNA and her own best evidence that [it] was helical.” Brenda Maddox, who wrote a biography of Franklin, described the photograph as “the clearest picture ever taken of the B form of DNA.” She also described Franklin setting it aside so that she could go back to working on the problem of the A form.
The new paper has two authors, a historian of science and a crystallographer. They are Alistair Sponsel, of the Science History Institute in Philadelphia, and Brian Sutton, of King’s College London. They reply to Judson very directly. In their words, the reason Photograph 51 shouted “helix” so clearly is that Rosalind Franklin meant it to.
One reason why Watson’s version survived for so long is that something is missing from the written record. Franklin usually kept careful and detailed laboratory notes, but she wrote very little about Photograph 51. Sponsel and Sutton therefore looked at the earlier image. They discovered that Franklin had written a great deal about Photograph 49, even though it had a defect in its appearance. As they interpret the evidence, she understood that the earlier photograph showed a helix. This was exactly the insight that Watson would later claim as his own, and it was the very reason she produced a second, improved version. Their conclusion is that Photograph 51 was made specifically so that it could be published. Some accounts have described it as a trial image that Franklin did not consider important, but in their view this is wrong.
Taking the picture again matches what colleagues have said about the way she worked. Franklin “was an experimental perfectionist,” according to the crystallographer Elspeth Garman. An image with a slipped film holder and a missing edge was clear enough to give Franklin information. According to this explanation, though, it was not clear enough for her to show to other people.
If she knew, why did she not hurry to publish? Sponsel and Sutton believe that her notes and her actions answer this question as well. They refer to a report she wrote in February 1952, in which she set out her scientific aims. DNA existed in two forms, called A and B. By the end of 1951, most people at King’s accepted that the B form was a helix. In May 1952, however, Franklin recorded an image that was not symmetrical, and after that she was no longer convinced that the A form was a helix. Wilkins often said that both forms were helical. In July 1952, as a practical joke on him, Franklin and Gosling wrote a funeral notice. It announced “the death, on Friday 18th July 1952 of DNA helix (crystalline)” and said they hoped Wilkins would “speak in memory of the late helix.”
She worked slowly because she chose to. All through 1952, she and Gosling carried out a long mathematical analysis of their X-ray pictures, which required a great deal of effort. Franklin was strongly opposed to building theoretical models before the data were available. “We are not going to speculate, we are going to wait, we are going to let the spots on this photograph tell us what the [DNA] structure is,” she said.
The spots were in fact leading her towards the answer. Her notebook shows that by February 1953 she had considered a helical structure for the B form. She was not yet sure how many strands it had, and she wrote: “Evidence for 2-chain (or 1-chain helix).” After her death, Aaron Klug studied her papers. At first he thought she had not been convinced of the double helix until she heard about the model built in Cambridge. Later, though, he found an original draft of her manuscript, dated 17 March 1953. It showed clearly that she had already arrived at the correct structure. The news of the model by Watson and Crick reached King’s on the following day. Sutton had already argued in 2023 that Franklin came close to the discovery. Her notes show that in early 1953 she was openly considering a helix with two chains.
On 25 April 1953, the journal Nature published three papers about the structure of DNA. The article by Watson and Crick mentioned Franklin only in a footnote. It said they had been “stimulated by a general knowledge of Franklin and Wilkins’ ‘unpublished’ contribution.” The directors of the two laboratories had made an agreement, and under it, papers by Wilkins and by Franklin, containing their X-ray data, appeared second and third in the same issue. As a result, these papers seemed to exist only to support the model. Later, Watson and Crick themselves stated that without Franklin’s data, “the formulation of our structure would have been most unlikely, if not impossible.”
Franklin died of ovarian cancer in 1958, at the age of 37. In 1962, the Nobel Prize in Physiology or Medicine was given to Crick, Watson and Wilkins. The prize is never given to someone who has died. Garman writes that Watson did not say “the Franklin photograph was the key event” until 1999. When The Double Helix was published, even the two men who shared the prize with him complained. Crick wrote to Watson that the book was misleading and in bad taste. Wilkins said that it was unfair to nearly everyone in it apart from Watson.
The physicist and historian Robert Crease once attended a series of lectures that Watson gave at Brookhaven National Laboratory. The first talk was about the events surrounding the discovery, and afterwards there was time for only one question. A woman put up her hand. “Dr Watson,” she asked, “I wonder if you could comment a little bit more on Rosalind Franklin’s contribution to the discovery of DNA.” Some people in the audience clapped.