\1% MR. GREGORY ON MECHANIC POWER. 



Indeed, much of Mr. H's reafoning, not only with refpeft 

 to the poft and the hat-peg, but throughout his paper, Teems 

 to reft upon a tacit adraiflion (not a direct avowal, it is (rue,) 

 of the erroneous notion, that forces exerted by animated 

 beings, and thole operating through the intervention of in- 

 animate things, are totally diftinct, and cannot be fubftituted 

 the one for the other, or have a fair comparifon inftituted 

 Familiar illuftra- between them. Whereas, on the contrary, not only the 

 theory but the practice of mechanics, proceeds ifpon the 

 principle, that thofe forces are equal in degree, however 

 different in their origin, or various in their mode of operation, 

 which produce equal effects. Thus, for a familiar example, 

 in the boring of a piece of ordnance ; the borer may either 

 be brought up to its proper polition in the gun by the action 

 of a man on the handles of a wheel, connected with the borer 

 by rack and pinion work, or by the action of a weight at- 

 tached to the farther end of a lever proceeding from the axle 

 of the fame wheel: and Mr. H. might as well deny the 

 poflibilily of the work performed being the fame in both thefe 

 cafes, as deny that a weight is kept from falling by an equal 

 force, when prevented either by an animal, or by a fixed in- 

 animate object ; or deny that there is an expenditure of me- 

 chanic power when a man counteracts the operation of gravity 

 upon his arm, when extended horizontally. While fpeaking 

 of the propofition which includes any fuch denial, we may 

 fafely apply to it Mr. H's own language ; — f A more errone- 

 ous propofition was never introduced into the theory or 

 practice of mechanics." 



Mr. Hornblower has taken the trouble of extracting feveral 

 paflages from the Article Machinery, Sup. Ency. Britan. 

 Miftakeof and among them has taken that which exhibits Profeflbr 

 Profeflbr Robi- Robjfon's meafure of" the exertion of a man, who walks at 

 the rate of 60 feet per minute, and raifes a weight of 30 

 pounds. The meafure 57600, which this gentleman thinks 

 enormoufly too large, is, in fact, loo fmall, in fo far as it 

 does not include that part of the exertion required by the man 

 to move himfelf. It was this omiffion of the learned Profeflbr 

 that induced me to lay down the general ftatement at p. 152 

 of your 43d Number, though I thought it might be deemed 

 inviduous if I fpecified my motives in that place. But when 

 Mr. H. had commenced the labour of extracting, it would 



furely 



