The photographs do not speculate. Neither should the diagrams that represent their findings.
What you're looking at
A horizontal spectrum with eight elements placed along it. The left pole is what the photograph itself shows — diffraction spots, measured angles, repeating distances. The right pole is what someone built with metal rods and their conviction that they'd solved it. Between them: measurements that require minimal interpretation (unit cell dimensions), geometric facts derivable from symmetry (the 34-angstrom helical repeat), chemical constraints that narrow the possibilities (Chargaff's base ratios), and finally the three-dimensional model that explains it all — but was not itself photographed.
Why I drew it this way
The spectrum format forces honesty about epistemological distance. I could have drawn a simple binary — "data" versus "theory" — but that would erase the middle ground where most working crystallographers actually live. The unit cell parameters are observed, but they require calculation from spot positions. The helical pitch is inferred, but it's inferred from geometry, not from wishful thinking. Chargaff's rules came from chemistry, not from my photographs, but they constrain what models are chemically plausible. The placement of each box reflects how many inferential steps separate it from the diffraction pattern itself. Green marks what I trust without reservation. Red marks what I cannot verify with my own apparatus.
What it argues
That the Watson-Crick model and Photograph 51 are not the same kind of object, and should not be drawn as if they were. One is a fact about how X-rays scatter off a fiber. The other is an elegant explanation, probably correct, built from many sources — some of them my photographs, some of them Chargaff's chemistry, some of them Watson's impatience and Crick's geometry. The diagram argues that we should label our inferences as inferences, not smuggle them into the data and pretend the crystal told us everything.
What I left out
I left out Wilkins, Pauling, and the entire social drama of who saw what and when. I left out the question of whether the model would have been built without my photograph, because that is a historical question, not a crystallographic one. I also left out the tobacco mosaic virus work I'll be starting at Birkbeck, which will produce equally beautiful diffraction patterns and no competing theorists with metal models. Some projects are quieter.