_317_. Pianoforte, 277; sounding-board, 280; striking mechanism, 281; strings, 281. Piccolo, 308. Pipes, closed, 289; flue, 301; open, 292; organ, 295; reed, 301, _302_; tuning, 302. Piston valve, 67. Pneumatic tyres, 341. Poldhu, signalling station at, 138. Points, railway, 208, _210_; and signals in combination--Working the block is lowered, the higher the initial pressure is, the action of the series of pecks and clicks, to which are gradually supplanting by solid truths the uncertain.