The planning, design and construction of a hydraulics laboratory – especially of a large one – can be a complicated procedure requiring specialized knowledge. The closed water circuit consists of an underground supply reservoir, a pumping station delivering water to high-head reservoirs, pipes discharging water from the reservoirs through discharge-measuring devices into flumes and models, and return channels delivering water back to the supply reservoir. The ‘starry sky’ procedure records wave orbits in models of harbours; it consists of photographing, with an exposure of one wave period, the reflection by the water surface of numerous points of light on the ceiling above the model. The size of the air bubbles and their velocity and direction are best measured by cinematographic or photographic methods. The measurement of the hydraulic characteristics of mixtures of solids and liquids is important in particular in the study of the hydraulic transport of solids through pipelines and for the operation of systems.