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Programmes have been devised for computing Patterson and Fourier syntheses in two and three dimensions with the EDSAC. An outline of the methods used is given and future possibilities are discussed. At present a two-dimensional summation of about 400 independent terms for about 2000 points takes'J hr. ; a three-dimensional summation of 2000 terms for 18,000 points takes 9 hr. A method~is"~lescribed whereby the EDSAC, without special modification, can be made to print results directly in contour form with considerable economy in time.
Bennett et al. (Tue,) studied this question.