PARTICULATE material is a general descriptive title for the many forms of matter existing in a state of sub-division into discrete particles. Such materials playan important part in almost all human activities, eitheras dust particles formed by natural agencies, or as powders produced by the artificial reduction in size of larger fragments of material. Dust is always present in the atmosphere, and though generally regarded as a nuisance,alsofulfils useful purposes ; but when present in excessive quantities it becomes a menace to health, and much active research is in progress to minimize the harmful effects of dust in mining and industrial atmospheres. Artificially ground powders are of the greatest importance to industry ; sometimes their production is the main objective, as in the manufacture of Portland cement or pigments,and fine grinding of immense tonnages is an essential stage in the reduction of metallic ores. The building industry uses large quantities of materials in powdered or granular form, and a knowledge of the size analysesof these is essential. Agriculture and civil engineeringare concerned with problems such as soil erosion, silt deposition and the foundations of buildings, for which data on the size characteristics of sedimentary deposits are needed. Thus there can be few manufacturing processeswhich are not dependent upon the use of powdered materials at some stage, and though the quantities involved maybe smaller than in the industries mentioned above, the monetary value may be high, as for example in the fabrication of parts from metal powders.