10 MR « GREGORY ON MECHANIC POWER. 



or by referring them to fome common meafure of ready ap- 

 preciation, that mechanics is made one of the mathematical 

 (ciences *. 

 Animal efforts , Thefe obfervations will enable us to fet Mr. H. " right as 

 mec&uiic power. to '^ identity o\' um trial exertion and mechanic power." Animal 

 efforts aie juftly confidered, both by the Mathematician and 

 the practical Engineer, as conftituting one fyecies of mechanic 

 power ; when thefe efforts give to bodies equal momenta, or 

 give to equal bodies equal velocities, it is truly faid the 

 animals exert equal forces; and we fay that animal power is 

 greater or lefs, as it is capable of imparting to bodies greater 

 or lefs momenta, or as it is capable of (lopping bodies moving" 

 with greater or lefs momenta : and the language of fcientific 

 men is analogous to this when they fpeak of any forces what- 

 ever. 

 Reply to Mr. It is now time to proceed to Mr. Hornblower's animadver- 



H's remarks on g^ U p 0n ^ ; n ft ance j adduced (and many others might be 

 nscat. adduced) to (hew that Mr. Smeaton's meafure of mechanical 



power and effect is not univerfally applicable. I afierted, 



* That Mr. Hornblower may not reft upon the mere authority 

 of any theoretic man, I beg to throw into this note an extraft 

 from the Median, que Philofojihiqi'.e of M. Prony ? an Engineer, who 

 unites with a profound acquaintance with the theory, an extenfive 

 practice, and whole example in this refpeft I fliould fmcerely rejoice 

 to fee more frequently imitated in this country. 



•* La nature de cette caufe de mouvemenr, nomme'e force ou 

 Jiutjfance\ nous eft tout-a-fait inconnue : Phomme appelle/o;YV? la 

 faculte organique qu'il a de fe mouvoir, de s'arreter, de produire 

 ou de fane ceiTer le mouvement des corps qui Penvironnent j et 

 fans favoir en quoi confifte cette faculte, il a fuppofe qu'il exiftait 

 ' quelque chefe de femblable dans les agens phyfiques qui font ou 

 qu'il cro t etre, fur le globe terreftre et dans Tunivers, les caufes 

 du mouvtment de d.fferens corps. Mais nous n'avons en me- 

 canique, aucun btfoin de connaltre la nature de la force owjirajjance 

 qui eft repiefer.tee, mefuree et introduite, dans le calcul, unique- 

 irtent par les effets qu'elle produit. Ces effets fe re*duifent toujours 

 a des veiefles que les puiflances ou tendent a donner, ou ont 

 effec~tivement donnees a de certaines maffes." M Parmi les diveii'es 

 puiffances que la nature nous offre, il en eft une tres remarquable 

 dent il convient de prendre les effets pour terrae de comparaifon 

 de ceux des autres puiffances \ c'dfc \a.fufanteur terrejirc a lafurface 

 de la terre/' &c. p. '20. 



that 



