146 THOMSON ON CARNOT'S 



ing graphical method of representing the mechan- 

 ical effect developed in the several operations, taken 

 from Mons. Clapeyron's paper, is extromely con- 

 venient. 



17. Let OX and OF be two lines ,t right angles 

 to one another. Along X measure off distances 

 ON^ , -ZVi JV a , N^Ns , N a 0, respectively proportional 

 to the spaces described by the piston during the 

 four successive operations described above; and, 

 with reference to these four operations respective- 

 ly, let the following constructions be made: 



(1) Along Y measure a length OA, to repre- 

 sent the pressure of the saturated vapor at the 

 temperature S m , and draw A A l parallel to OX, and 

 let it meet an ordinate through N^ , in A l . 



(2) Draw a curve A^PA such that, if ON repre- 

 sent, at any instant during the second operation, 

 the distance of the piston from its primitive posi- 

 tion, NP shall represent the pressure of the vapor 

 at the same instant. 



(3) Through A^ draw A Z A 3 parallel to OX, and 

 let it meet an ordinate through N z in A 9 . 



(4) Draw the curve A 3 A such that the abscissa 

 and ordinate of any point in it may represent re- 

 spectively the distances of the piston from its 

 primitive position, and the pressure of the vapor, 

 at each instant during the fourth operation. The 



