AT the present time, the investigation of atmo-spheric pollution—conducted in Great Britain by the Department of Scientific and Industrial Research through the agency of a Research Committee—is mainly carried out with the aid of three instruments, all designed by Dr. J. S. Owens, Superintendent of Observations to the Committee. The first, known as the deposit gauge, is designed for the purpose of measuring the total amount of impurity deposited on a given area. It consists essentially of a rain-gauge, in which the ordinary copper collecting funnel is replaced by a large glass receiver. The rain, with the impurity, is collected for a definite period, usually a calendar month, and then analysed. The second and third instruments are respectively the automatic air filter and the jet dust counter. The former gives a semi-continuous record of the concentration of suspended impurity in the atmosphere. The latter provides a means of determining the number of solid particles in a given volume of air and of ascertaining the physical nature of the individual particles. Dr. Owens has recently made important improvements to both these instruments, and, although no new principles are involved, their range of usefulness has been very greatly extended.