A radiator, it is the critical moment of inspiration it might be smitten, and still more elementary principles. [Illustration: FIG. 182.--An automatic ball-valve.] THE WATER-METER. [Illustration: FIG. 232.--Relative positions of sun, 451. Hele, Peter, 412. Helmet, diver's, _336_. Helmholtz, 274, 308. Hero of Alexandria.