Farrow's military encyclopedia : a dictionary of military knowledge . re. When steam isallowedto enter, the indicator piston rises against the re-sistance of the spring to a height corresponding tothe steam pressure, and if this pressure remains un-changed during a stroke, a straight line parallel tothe atmospheric line will be traced ; when releasetakes place the piston instantly falls and the pencilmoves with it, and when a return stroke of the en-gine occurs, the pencil will trace a line correspond-ing to the back pressure against which the enginepiston is moving. This gives an idea of the
Farrow's military encyclopedia : a dictionary of military knowledge . re. When steam isallowedto enter, the indicator piston rises against the re-sistance of the spring to a height corresponding tothe steam pressure, and if this pressure remains un-changed during a stroke, a straight line parallel tothe atmospheric line will be traced ; when releasetakes place the piston instantly falls and the pencilmoves with it, and when a return stroke of the en-gine occurs, the pencil will trace a line correspond-ing to the back pressure against which the enginepiston is moving. This gives an idea of the processof tracing a diagram when steam follows full .stroke ;when a cut-olT is used, tlur pencil traces the sameline as before until the cut-off valve closes, when,as the pressures fall, then is traced a curve whichirives the pressure at each point of the forward mo-tion according to the law for expansion of length of a diagram drawn in this way repre-sents on a smaller .scale the stroke of the engine, andthe line traced by the iimi il shows the pressures. Fig. upon the piston. These pressures are mea-sured by the movement of the spring containeii inthe indicator, an inch of movement, or an inch ofheight above the atmospheric line on the diagram,representing so many pounds pressure, accordlmr tothe spring used; thus a 30 lb. spring would be com-pressed, so as to give the pencil a movement of one nroiCATOK RING. 96 INDUCTION OF ELECTRIC CURRENTS. incli for 30 lbs. steam pressure, and a 40 lb. spring,one inch for 40 lbs. pressure, and so on. Havingthen, a scale, in which one inch is divided into 30 or40 parts, or any other numlter of parts such as or-dinarily used, we can readily measure any pressuredrectly from the diagram when once we are permit-ted toknow what scale or spring has been employed. Fig. 3 shows a neat construction ofthe theoretical expansion curve, whichshould always be drawn upon the dia-gram in order to compare it with theactual line traced by
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Keywords: ., bookcentury1800, bookdecade188, booksubjectmilitaryartandscience
