Electronic+Richards+Box+Systems

Before computer graphics could do the job, mechanical methods were used to fit large molecules to their electron density maps. Using techniques of X-ray crystallography crystal of a substance were bombarded with x-rays, and the diffracted beams that came off were assembled by computer using a Fourier transform into a usually blurry 3-D image of the molecule, made visible by drawing contour circles around high electron density to produce a contoured electron density map. In the earliest days contoured electron density maps were hand drawn on large plastic sheets. Sometimes bingo chips were placed on the plastic sheets where atoms were interpreted to be. This was superseded by the Richards Box (see picture here) in which an adjustable brass Kendrew molecular model was placed front of a 2-way mirror, behind which were plastic sheets of the electron density map. This optically superimposed the molecular model and the electron density map. The model was moved to within the contour lines of the superimposed map. Then, atomic coordinates were recorded using a plumb bob and a meter stick.