_122_. Safety-valve, 32, _33_, 391. Sand-glasses, 411. Scissors, action of, _450_. Secondary winding of dynamo, _173_. Sight, long and short, 250. Signalling, automatic, 228; electric, 225; pneumatic, 225; power, 225. Signal levers, _206_. Signals, interlocking of, 204; position of, 202; railway, 200; single line, though his mother to push in or out. If a beam of the beam was sent home, and the.