MR. GREGORY ON MECHANIC POWER. [\ 



that a horfe (landing ftill and fuftaining a weight which hung Reply to Mr. 



by a cord over a fixed pulley, would, after a due interval of H . s rema '' ks0 » 

 7 r ' a former ftate- 



time, be completely fatigued, althoagh neither the animal nor men t f 



the weight moved, and that, of conlequence, there was a 

 power expended, of which Mr. Smeaton's rule did not furnilh 

 an adequate meafure. Mr. H. as though he underftood me 

 to affirm, that fatigue was the only indication of mechanical 

 power expended, inftead of limiting it to animal efforts as the 

 connection evidently required, exclaims, M it is really difficult 

 to be grave on this occafion:" p. 268. and argues in a kind of 

 exulting ftrain which favours a little, I am afraid, of the Ipirit 

 alluded to in the French proverb, Chanter le iriomphe avant 

 la vidloire ! Let us, fays this gentleman, have a " poft inftead 

 of the horfe, and furely that will not tire, and what will be 

 the confequence then ? why then there will be no power 

 expended, and no effecl produced." Mr. H. then, it would 

 feem, has forgotten that the poft is retained in its fituation by 

 a force which in this cafe oppofes that of gravity acling upon 

 the fufpended weight. The cord running over the pulley and 

 fuftaining the weight, being fattened to the poft, would move 

 it, were it not that the cohefive force of the earth in which the 

 poft is fixed, changes the ftate into which the poft would be 

 brought by the action of gravity upon the weight, and is 

 fufficient to retain the whole at reft. If the poft were fet in 

 loofe fand, or in a quagmire, the weight would draw it away, 

 and then I fuppofe, even according to Mr. H's notion, there 

 would be a power expended, and an effect produced. So 

 likewife, in Mr. H's other example, of the hat hung upon the 

 pin, the force of gravity is balanced by the cohefive force of 

 the wood or other matter, into which the pin is fixed. But it 

 would be egregious trifling to dwell much longer upon fuch in- 

 stances as thefe. Mr. H. conceives, if I have not completely 

 pifunderftood his meaning, that there is no " mechanical 

 power" that is not '* made up of a mafs of matter moving 

 with a determinate velocity ;" and as fuch an opinion mu ft 

 either arife from neglecting to difcriminate between caufe and 

 effect, or from a virtual denial of the whole docVines of 

 italics, (in which powers are excited without any motion 

 being produced,) I {hall hope to be excufed though 1 wafte 

 bo time on a refutation of any fuch pofttion. 



Indeed, 



