Abstract: The present method provides a determination of physical characteristics of materials. For example, the granulometry of a falling or flowing stream of disperse material may be analytically determined by a heat image camera cooperating with a memory such as a screen type image storage, a monitor, and a process computer such as a microcomputer which compares the measured values with a reference value to provide a control signal. A control apparatus regulates the flow rate of the material stream, such as aggregate, in response to said control signal. The present method may be used to determine, for example, the size of falling liquid droplets or the size of the particles of granular material which is stationary in a measuring zone or space.