A comparison has been made between three methods, given in the title, for the detection of weak x‐rays. The secondary electron multiplier tube has a lower resolving time than the Geiger‐Mueller tube, but the G‐M tube is from 5 to 10 times as sensitive to x‐rays of the wave‐lengths here studied, 0.63A to 1.54A. A diffraction pattern of a liquid can be obtained with a G‐M counter in roughly one‐twentieth the time taken for a photographic exposure.