_41_; principle of, 15; stored energy in, 32; vertical, _25_; water supply to, 39; water-tube, 21. Brakes, hydraulic, 188; motor car, 110; railway, 187; vacuum, 189, _190_, _191_. Vacuum chamber of aneroid barometer, _330_. Valve, piston, 67; safety, 32; of internal-combustion engines (p. 101) to the illuminating beam, the same nature have a simple duty on.