. A text book of physics, for the use of students of science and engineering . a travel topermit of direct connection to the indicator drum. An arrangementsuch as is shown in Fig. 469 is often used. The crosshead C drives alever AB to which it is connected by a short link BC. The indicatorcord is attached at D, and thus the drum obtains the motion of thepiston on a reduced scale. The pipe arrangement and cock at E andF enable the indicator to be connected to either end of the cylinder ; ja diagram from each end is generally taken on the same paper.)Such a diagram is shown in Fig. 470. The frac
. A text book of physics, for the use of students of science and engineering . a travel topermit of direct connection to the indicator drum. An arrangementsuch as is shown in Fig. 469 is often used. The crosshead C drives alever AB to which it is connected by a short link BC. The indicatorcord is attached at D, and thus the drum obtains the motion of thepiston on a reduced scale. The pipe arrangement and cock at E andF enable the indicator to be connected to either end of the cylinder ; ja diagram from each end is generally taken on the same paper.)Such a diagram is shown in Fig. 470. The fraction s0 means thatthe strengthof the spring used in the indicator was such that the XXXIX BRAKE HORSE POWER 513 scale of pressures on the diagram is 80 lb. wt. per square inch foreach inch of vertical height. From the diagrams, the mean pressurefor one side of the piston is 64 and for the other side 60 ; the averagefor both sides is thus 62 lb. wt. per square inch. It is obviouslyimpossible for the indicator to draw the perfect vacuum line on the St Q0 2 £ J2 f£ NO 3 00 O. / I oTop so l! si h^^ R 3 o A L O Nf Fig. 470.—Example of an indicator card. paper. The line AL is drawn by putting the indicator cylinder intocommunication with the atmosphere by means of the cock ; AL thusrepresents the pressure of the atmosphere. If the perfect vacuumline is required, it may be drawn on the diagram at a distance belowAL equal (to scale) to the pressure of the atmosphere, obtained byreading the barometer at the time the diagram was taken. Brake horse-power.—The indicated horse-power of an engine isa measure of the power developed on the piston of the engine, anddoes not represent the power which the engine is capable of givingout in the useful form of driving machinery. To obtain the latter,the energy given out by the engine may be absorbed by the resistanceoffered by a brake. A type of brake suitable for testing enginesof comparatively small power is shown in Fig. 471. A
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Keywords: ., bookcentury1900, bookdecade1910, bookpublishe, booksubjectphysics
