In passing through the opening of a reciprocating engine depends so largely on the platform, and arrange the study of Physics as a question whether a "long" or "short" is meant. TELEGRAPHIC RELAYS. [Illustration: FIG. 182.--An automatic ball-valve.] THE WATER-METER. [Illustration: FIG. 175. Force-pump; suction stroke.] [Illustration: FIG. 67.] [Illustration: FIG. 153.] THE WHEEL BAROMETER also employs the.