2 Wilson and Noble, Entropy Diagrams. 



quantity of mixture throughout the combined diagrams, 

 instead of an amount which varies in different parts of the 

 figure, will be generally admitted ; and, with respect to 

 indicator diagrams, methods of eliminating the effect of 

 clearance have been proposed and used for many years 

 by different engineers. In this connection, the construc- 

 tions advocated by A. C. Kirk\ W. Schonheyder^, Professor 

 Unwin'', and Prof Osborne Reynolds^ may all be men- 

 tioned. In the case of entropy diagrams, the hypothetical 

 diagram for one pound of steam was discussed by Willans, 

 but the authors have been unable to find any actual dia- 

 grams in which any method of reduction was given, or in 

 which any reductions of this nature have been made. 

 Without laying down any opinion as to the practical 

 utility of entropy diagrams, founded, as they are, upon 

 assumptions which are regarded by many as questionable, 

 it may, nevertheless, serve a useful purpose to call atten- 

 tion to the above point, and to indicate a method whereby, 

 without any serious amount of labour, this required 

 reduction can be performed. The pro. and entropy dia- 

 grams will then represent the changes which take place 

 in one pound of mixture passing through the engine, and 

 hence admit of direct comparison with the diagrams 

 obtained from any other engine in a manner which is not 

 possible under the present system. 



It may here be recalled that, if the indicator card is to 

 disclose anything relating to the quality of the mixture, 

 it is necessary that its expansion line shall be placed in 

 the correct position, with respect to the corresponding 

 saturated steam curve for that quantity of steam and 



' Trans. Inst. Naval Architects. . Vol. xxiii. (1S82), p. 33. 



2 Proc. Inst. C.E. Vol. xciii., p. 230. 

 ' „ „ ,, p. 208. 



* ,, ,, Vol. xc, p. 31. 



