How does DNA look like?

The shape of DNA was not discovered by any super-biological microscope but by Physics methods.

J.D. Watson and F.H.C. Crick in 1958 observing quite a complicated X-ray interferograms of the DNA crystals, wondered if it were a single or a double spiral. Finally, their choice was correct what awarded them with a Nobel prize in 1962.

X-ray picture of the natrium salt of the DNA [Source: Encyklopedia of Modern Physics, Warsaw, PWN]