Page:Reflections on the Motive Power of Heat.djvu/170

146 graphical method of representing the mechanical effect developed in the several operations, taken from Mons. Clapeyron's paper, is extremely convenient.

17. Let OX and OY be two lines at right angles to one another. Along OX measure off distances ON1, N1 N2 , N2 N3 , N3 O, respectively proportional to the spaces described by the piston during the four successive operations described above; and, with reference to these four operations respectively, let the following constructions be made:

(1) Along OY measure a length OA, to represent the pressure of the saturated vapor at the temperature S; and draw AA1  parallel to OX, and let it meet an ordinate through N1 , in A1 .

(2) Draw a curve A1 PA such that, if ON represent, at any instant during the second operation, the distance of the piston from its primitive position, NP shall represent the pressure of the vapor at the same instant.

(3) Through A2  draw A2 A3  parallel to OX, and let it meet an ordinate through N3  in A3 .

(4) Draw the curve A3 A such that the abscissa and ordinate of any point in it may represent respectively the distances of the piston from its primitive position, and the pressure of the vapor, at each instant during the fourth operation. The