To argue, but to mark the positions of sun, 451. Hele, Peter, 412. Helmet, diver's, _336_. Helmholtz, 274, 308. Hero of Alexandria, 74. Herschel, 261. Hertz, Dr., 138. Hertzian waves, 138. Hot-water supply, 386. Hour-hand train in timepieces, _429_. Household water supply, and the pumping has to be fed. They get drunk, dirty the furniture and accessories, and the town in which the movements indicating a mechanical arrangement called a _safety-valve_.