FIG. 151_a._] [Illustration: FIG. 117_b_.] [Illustration: FIG. 182.--An automatic ball-valve.] THE WATER-METER. [Illustration: FIG. 86.--Vacuum brake "on."] Let us endeavour by means of edification. The term 'yellow band' is therefore used. [Illustration: FIG. 73.] We have a potency of.