Setup of Laue, Friedrich and Knipping. The source of Röntgen's radiation is separated from the crystal under investigation by a lead screen, S, pierced at B1, and a series of ever-finer lead diaphragms B2 (in the lead chamber K), B3 and B4. Around the crystal Kr photographic plates may be placed at various positions P1–5. The extension R is added to trap the straightforwardly passing rays and obviate disturbing secondary rays of the wall. For precision measurements there is a diaphragm Ab for the pinhole B1 in screen S (Friedrich et al., 1912).