Abstract
UNDER this title, Robertson1 has published a simple optical method of constructing Patterson diagrams. Hagg2 has suggested a modification of this method. Bragg3 described a further improvement by the introduction of a lens in the path of the light rays, so that both patterns, the diagram of which is required, are on the same scale. The Patterson is then formed in the focal plane of the lens, and can be photographed, viewed on a screen or with the aid of an eyepiece. The whole arrangement then consists of an ordinary camera or telescope, in front of which are held two identical and properly oriented patterns. The scale of the Patterson can be varied by varying the distance in between the patterns. If the aperture of the lens is made large enough to accommodate all the relevant rays, the second screen need not be in contact with the lens. If punched screens are used, the only disadvantage is the lack of continuous adjustment of the pattern, possible in the original sphere and thread method of Robertson.
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