A recording, photometric particle‐size analyzer has been developed which is useful in comparing the particle‐size distributions of dusts in the subsieve range. The instrument follows the progress of the sedimentation of a suspension by means of a collimated beam. Provision for continuously varying the sedimentation depth allows analysis of the entire range within 1 hr. The optical system and temperature control were designed to increase the accuracy of analysis of the finer particles. A simplified system is given for calibrating the sedimentation curves in terms of particle size.