336 APPLIED SCIENCE 



^..'General Conclusions. The most important conclusion to 

 be drawn from the foregoing examples is, that the investigation 

 of the efficiency of any given direct-acting engine is rendered 

 comparatively easy by the new method. Next in importance 

 may be ranked the warning not to judge hastily as to the result 

 of any given modification in proportions or speed. The differ- 

 ences introduced by a change of speed are especially remark- 

 able, and show how futile reasoning must be as to relative 

 efforts and resistances or to stresses on the various parts of the 

 engine, or to the efficiency of any design when the inertia of the 

 masses is left out of the calculation. 



Further conclusions may be drawn as follows : 1st, that 

 high speeds do not necessarily involve small efficiency ; 2nd, that 

 a short connecting rod is not very disadvantageous ; 3rd, that 

 expansive working, even when carried to great lengths, does not 

 necessarily involve a loss of efficiency. 



Table I. gives an abstract of the numerical values obtained 

 with this particular engine, but the reader must be warned 

 against considering these results as generally applicable to other 

 engines of different proportions. 



The necessary calculations and drawings for this paper have 

 been made by my assistant, Mr. J. A. EWING, to whom I am 

 much indebted both for the accuracy with which the work has 

 been done, and for the interest he has shown in adopting the 

 novel method of investigation. 



The Appendix contains data which will allow the reader 

 to verify the results arrived at without going through all the 

 calculations. 



This Appendix has been drawn up by Mr. EWING. 



APPENDIX TO PART II. 



On the Application of Graphic Methods to the Determination of the 

 Efficiency of Machinery. 



To determine the forces required for the acceleration of the 

 piston and connecting rod in each position of the engine, we must 

 know the acceleration of the piston, and the angular velocity and 



