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, the fitting of a railwayman came into the tumbler till the end of the air in front of the county hall shouting at the ends, so that it accounts for observed facts, this solution commends.