Rotatory Steam-Engine. 57 



my, on account of this very attrition from a centre, which we con- 

 sider to be ruinous to every steam-engine on a revolving principle. 



The application of the result of this illustrative experiment 

 to the subject in question, is abundantly obvious, the circum- 

 stance of rotation from a centre, with pressure on bearing sur- 

 faces of which the parts are at unequal distances from the 

 centre, implies the excessive attrition of the circumferential 

 surfaces above those which are near the centre, and which move 

 with less velocity. Hence the circumferential surfaces wear 

 more rapidly, and are unfit for use long before the central parts 

 have suffered any sensible effect. Where extensive metallic 

 surfaces are in contact, their repair is a matter of much ex- 

 pense and delay. 



To diminish this cause, or to delay its effect, the revolving 

 piston is removed far from the centre of action. By this means, 

 however, the bulk of the machine, and its friction, are very 

 much increased, and the evil only partially remedied. It is 

 obvious, however, that in this way, by increasing the radius, 

 the engine is brought more nearly to the principle of the straight 

 cylinder ; so that perfection would just be attained if the cir- 

 cular cylinder were made straight, or, in other words, if the rota- 

 tory engine were converted into an ordinary reciprocating engine. 



When a piston reciprocates in a straight cylinder, all its 

 points, and those of the cylinder, move equally, being in lines 

 parallel to the axis ; and to prevent accumulation of eccentri- 

 city, the piston may have its position on the circumference al- 

 tered by part of a turn. 



The essential nature of rotatory attrition is therefore fatal to 

 the success of the revolving principle, — a cause of expensive 

 repairs, and speedy destruction. 



IV. There are other defects to which this species of engine 

 is peculiarly liable ; — to vacuities and losses at the valves and 

 passages — to irregular action, and collisions and shocks from 

 the action of the parts upon one another ; but these will be the 

 subject of consideration as they occur in individual machines. 



V. Unless, therefore, we shall find that there is some pecu- 

 liar applicability in this form of engine above the common one, 

 to certain important purposes, such as steam navigation and in- 

 land transport, we must abandon the hope of deriving practi- 

 cal advantage from the engine of rotation. 



