. The elements of railroad engineering . it downwards to thispoint will be 4,518 — 2,309 = 2,209 pounds. PNEUMATICS. 427 1070. The Baroscope.—The buoyant effect of air isvery clearly shown by means of an instrument called thebaroscope, shown in Fig. consists of a scale beam, fromone extremity of which is sus-pended a small weight, and fromthe other a hollow copper air they exactly balance eachother; but Avhen placed under thereceiver of an air pump and theair exhausted, the sphere sinks,showing that it is really heavierthan the small weight. Beforethe air is exhausted, each bo
. The elements of railroad engineering . it downwards to thispoint will be 4,518 — 2,309 = 2,209 pounds. PNEUMATICS. 427 1070. The Baroscope.—The buoyant effect of air isvery clearly shown by means of an instrument called thebaroscope, shown in Fig. consists of a scale beam, fromone extremity of which is sus-pended a small weight, and fromthe other a hollow copper air they exactly balance eachother; but Avhen placed under thereceiver of an air pump and theair exhausted, the sphere sinks,showing that it is really heavierthan the small weight. Beforethe air is exhausted, each bodyis buoyed up by the weight ofthe air it displaces, and since the fig. 197. sphere displaces the most air, it loses more weight by reasonof this displacement than the small weight. Suppose thatthe volume of the sphere exceeds that of the weight by 10cubic inches; the weight of this volume of air is this weight be added to the small weight, it will overbal-ance the sphere in air, but will exactly balance it in AIR COMPRESSORS. 1071. For many purposes compressed air is preferableto steam or other gas for use as a motive power. In suchcases air compressors are used to compress the air. Theseare made in many forms, but the most common one is toplace a cylinder, called the air cylinder^ in front of the cross-head of a steam engine, so that the piston of the air cylindercan be driven by attaching its piston rod to the cross-head,in a inanner similar to a steam pump. A cross-section ofthe air cylinder of a compressor of this kind is shown in , in which A is the piston and B is the piston rod, drivenby the cross-head of a steam engine not shown in the ends of the lower half of the cylinder are fitted withinlet valves D and D\ which allow the air to enter the 428 PNEUMATICS. cylinder, and both ends of the upper half are fitted withdischarge valves F and F\ which allow the air to escapefrom the cylinder after it has been compressed to there
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectrailroadengineering
