822 Transactions of tee American Institute. 



action of the reciprocating parts of a steam-engine, which, so 

 far as he has pursued the subject, leads him to results not dis- 

 similar to those to which the present inquiry has conducted. Upon 

 certain points, however, he has expressed himself in such a manner as 

 to convey impressions which he probably did not intend ; and thus, 

 perhaps, to excite in some minds doubts of his substantially just con- 

 clusions. The natural effect has been to create the belief, in which 

 the undersigned to some extent at first participated, that the problem 

 presented in this engine is more obscure than, upon closer examina- 

 tion, it is found to be. 



The particular points of Mr. Porter's articles to which refer- 

 ence is here made, are : First. The stress laid by him upon the 

 fact that the strain upon the crank produced by the living force 

 ©f the piston at the end of the stroke (revolution supposed to be 

 uniform) is equal to the centrifugal force which a mass of equal 

 weight would exert, if revolving with the same velocity at the 

 end of the crank. Secondly. The inference which seems to be 

 drawn from this, that the heavy piston high speed steam-engine 

 is closely analogous in its action to a rotary; or, in Mr. Porter's 

 own words, that " by combining rapid speed and short stroke 

 with considerable weight in these parts (the reciprocating parts) their 

 centrifugal force may be developed to whatever extent we choose ; 

 and if it is in excess of the steam, the engine, with the steam turned 

 on, becomes in effect a rotary engine ;" and thirdly, the proposition 

 that " the excessively intermittent pressure caused by working steam 

 at a high grade of expansion is transformed (in this engine), as by 

 magic, into a steady and uniform rotative pressure upon the crank."' 



The second and third of these propositions are hardly borne out by 

 the analysis. To what extent the first is so, will be apparent from 

 considering the diagram here presented : 



If a heavy body, A, 

 revolve about the cen- 

 ter, B, at the extremity 

 of the arm, A B, it will 

 exert upon this arm an 

 equal centrifugal force 

 at every point of the 

 revolution. If the same 

 body be at the same time connected with the arm, C D, equal to A B, 

 and similarly situated in reference to the center, D, the connecting rod 

 A B and the arm C D being both void of weight, then at C there will 



