This paper gives the formulae for the Fourier transforms of a number of helical structures, and provides evidence that the structure of a synthetic polypeptide was based on the alpha helix of Pauling and Corey. "It was, I believe, the first fairly conclusive experimental evidence for the existence of a helical structure at the molecular level.... The value of this work, seen in retrospect, is that it was a first step on the road to the discovery of the structure of DNA by Jim Watson and Crick" (Cochran, "This week's citation classic," Current Contents, May 18, 1987, 16).