A cylindrical x‐ray camera of about 57 mm diameter has been designed which may be used for powder photographs (Hull‐Debye‐Scherrer method) up to 1000°C or down to liquid air temperatures. Convenience in use is obtained by placing the film on the outside rather than the inside. Using a Siegbahn type x‐ray tube with Cu or Fe anticathode and 15 to 20 milliamperes tubes current, good diagrams may be obtained in ten minutes to two hours depending on the substance being investigated. The method permits the study of those crystal modifications which are stable at high or low temperatures but unstable at room temperature. Lattice constants may be determined to an accuracy of 0.2 percent.