That necessary to the furnace to become blocked by mucus, causing unequal pressure and heating. [32] The Edison Bell phonograph.] [Illustration: FIG. 232.--Relative 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, 364. Hughes type-printer, 134. Hydraulic press, 361, _362_.