Linus Pauling showed evidence for a helix and planar base stacking along the helix axis. Early in 1953 Watson and Crick proposed a correct structure for the DNA double helix. Pauling later cited several reasons to explain how he had been misled about the structure of DNA, among them misleading density data and the lack of high quality X-ray diffraction photographs. During the time Pauling was researching the problem, Rosalind Franklin in England was creating the world's best images. They were key to Watson's and Crick's success. Pauling did not see them before devising his mistaken DNA structure, although his assistant Robert
Maurice Wilkins the helical nature of the A-form. In early 1953 Watson visited King's College and Wilkins showed him a high quality image of the B-form X-ray diffraction pattern, now identified as photograph 51, that Franklin had produced in March 1952. With the knowledge that Pauling was working on DNA and had submitted a model of DNA for publication, Watson and Crick mounted one more concentrated effort to deduce the structure of DNA. Through Max Perutz, his thesis supervisor, Crick gained access to a progress report from King's College that included useful information from Franklin about the features of DNA she had