Abstract: The invention is employed for evaluating particles, such as droplets of aerosol sprays suspended in a gaseous medium. A stream of the particles to be analyzed is flowed into a narrow sample zone across the optical axis of a beam of light. Scattered radiation from the particles is focused on the image plane in which a photosensitive surface is located. Images of particles formed there are reproduced on a fluorescent or phosphorescent display screen of a cathode ray tube. A scale on the screen is employed for measuring the dimensions of the particles. The confinement of the stream of the mixture to about the depth of focus of the objective lens of the camera reduces effects of out-of-focus particles and permits evaluation of individual particles.