text: what evidence did james watson and francis crick use to deduce the structure of dna.?   graemew mentioned rosaline franklin and he is exactly right to do so!  without her work with x ray defraction, which francis and crick stole from her, they probably wouldn't have been the discoverers of the dna double helix structure.  linus pauling probably would have beaten them to it. franklin took a "picture" of the structure of dna that showed its structure to be a double helix.  they knew the chemical compostion from tests that had been run, and they figured up the pairing of the bases by using cardboard cut outs.