THE INERTIA OF THE CONNECTING ROD — MACGREGOR. 193 



VIII. — (3n the Graphical Treatment of the Inertia of the 

 Connecting Rod — By Prof. J. G. MacGregor, D. Sc, 

 Dalhousie College, Halifax, N. S. 



{Received June 15th, 1S92). 



In slow-speed steam engines, no great error is introduced in 

 calculating the effort of the connecting rod on the crank-pin, on 

 the assumption that the connecting rod is without mass. In 

 high-speed engines, however, a considerable error is thus intro- 

 duced ; and it is therefore desirable to hav^e a method of deter- 

 mining the actual effort. In this paper a graphical method of 

 making the determination is described. 



The effort transmitted by the connecting rod is affected by the 

 weight of the rod as well as l)y its inertia, and also by the fric- 

 tion of the surfaces in contact. The effect of the weight of the 

 rod and of friction, however, ma}^ be found by well known 

 methods. I shall therefore assume the rod to be weightless 

 (though not massless), and the surfaces in contact to be smooth. 



Let CA be the centre 

 line of the crank of the 

 ordinary steam engine, 

 and AB that of the 

 connecting rod, BC be- 

 ing thus the line of the 

 piston's motion. The 

 end B oi AB there- 

 ^, fore moves to and fro 



■^^^'^- in the line BC, while 



the crank-pin A moves in the circle A^ A^ A_. The motion of 

 these points is regulated by the flywheel. If the engine have a 

 flywheel of sufficiently great moment of inertia, A will move in 

 its circle with practically uniform speed. If the moment of 



