A 1929 technical article by Professor E. Goldberg describing the spectrodensograph, an instrument that automatically records the absorption curves of dyestuffs. It explains the optical layout (monochromator coupled to a spectrophotometer, grey wedge, twin prism), the registering table and pin that prick the curve onto graph paper, and the method of measurement. It also covers measuring dyed paper and fabric by reflected light and lists the instrument's advantages over conventional spectrophotometers. Illustrated with eight figures of the apparatus and ray paths.