Rotatory Steam-Engine. 49 



mover progresses in its reciprocal strokes in the cylinder. How 

 is this gradual change from rest to motion, and from motion to 

 rest, to be rendered consistent with uniform motion communi- 

 cated to the crank in its circle ? it is not only consistent with 

 it, but consequent upon it. It is to this very graduation of rec- 

 tilineal motion, that the uniform circular motion contributes, 

 and it is with such alone that it could be any degree consistent. 



To trace the simultaneous positions of the point describing the 

 circle of the crank, and the point describing the straight line 

 in the cylinder, it is necessary that we have recourse to a simple 

 diagram. You are requested to conceive a circle with its centre 

 and radius placed at a given distance from the end of the cy- 

 linder, so that a piston moving in the given straight line of its 

 piston-rod, at a given distance from it, is so connected with it 

 that the motion of the one produces the motion of the other. 



Let Figs. 5 and 6 represent a cylinder, and the Circles 1, 5, 

 10, 15, and 20, the path of the crank, the numerals on the cy- 



Fig.5. 



Fig. 6. 



D is\ 



Disl 



5B 



Under and on the circles representing corresponding places of 

 the crank and the piston at given instants of time. In Fig. 5, 

 the motion of the crank is supposed uniform, and the circle di- 

 vided into equal parts, while in Fig. 6 the axis of the cylinder 

 is supposed to be divided into equal parts to represent a hypo- 



VOL. XXIV. NO. XLVII. — JANUARY 1838. D 



