Abstract: A photoacoustic effect is used in order to measure a flow rate of a flowing medium (M), in particular of natural gas. A light emitter (1) is used to produce in the medium (M) a sound wave (S) which is transmitted by the medium (M) and detected by a sound detector (2). The light emitter (1) is less exposed to the medium (M) than a diaphragm such as used in the ultrasonic method.

Abstract: A moving body surface or paper web (1) to be investigated is irradiated at at least one irradiation site by 3 laser light sources of a surface structure measuring device (FOS1, FOS2). Reflected and scattered light is detected and evaluated in order to calculate ellipse points. An ellipse major axis ratio corresponding to a fiber orientation ratio, and a fiber orientation angle are calculated from the ellipse parameters thus obtained. Identical measurements and calculations are carried out periodically on an isotropic sample (NO) and a sample (Nx) having a fiber orientation similar to that of the body surface to be measured, in order to calibrate the measurements at the body surface (1).