Rectangular piece of acetate film containing negative images of two X-ray diffraction patterns of DNA. Both images were created by Rosalind Franklin (1920-1958) and Raymond Gosling (1926-2015) at King’s College London in 1952. The image on the left, which shows the “A” form of DNA, was number 42 in Franklin’s series of experimental DNA images. The image on the right, which shows the “B” form, came fifty-first in the same series. Later known as “Photograph 51,” it was published in Franklin and Gosling’s 1953 Nature article “Molecular Configuration in Sodium Thymonucleate” alongside the article in which James Watson and Francis Crick proposed the double-helix structure of DNA.