Rotatorif Steam-Engine. SI 



95 per cent. ; and at the fifth division, having completed one 

 quarter of a revolution, the pressure is for an instant equal to 

 100 per cent, or the whole power on the piston ; but the action 

 has now become a maximum. In its next point a diminution of 

 circular force takes place : at the sixth division the force has 

 diminished by 5 per cent. ; at the seventh 19 per cent, are lost 

 (apparently) ; at the eighth 41 per cent. ; at the ninth 69 per 

 per cent, are lost ; and at the tenth the piston has reached the 

 end of its stroke, and the whole pressure applied to the crank, 

 in this position, would produce no effect at all on the circular 

 orbit, or the apparent loss would be 100 per cent. Equal 

 diminutions take place through the remaining semicircle during 

 the returning stroke of the ascending piston. 



The following table of the part of the power directly avail- 

 able to the production of circular motion at ten points in the 

 semicircle, may therefore be found. 



Such is the reasoning by which, with apparently correct 

 steps, many have been led to the conclusion, that, in the crank, 

 the mean effect is less (by more than one-third) than the pres- 

 sure exerted in the cylinder by means of the piston. 



I have gone into an analysis of this false reasoning the more 

 fully, as it puts more perfectly before the mind of the reader 

 the circumstances in which the error of the conclusion lurks in 

 concealment. I shall proceed immediately to lay open the 

 source of error, and the means of arriving at the truth. 



Let it then be recollected, that, in all calculations of power, 

 we must attend to space passed over, as well as to the force 

 exerted in that space. And that a force of two pounds, moving 

 a weight of two pounds through three feet a second, is equal in 



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