270 MECHANIC POWER. 



Weafureof WQuId exprefs the produaion or efFed by 30x1920 or 

 njech.nic power ^^^^ .1 r r , , - , • . - ,* 



oreffca* 5760 as the mealure or the mairs exertion daring the minute. 



Sir, it is more than even one oF Boulton and Walts' horfes can 

 do.— Well may he fay, '* fuch an exertion will completely 

 > exhaufl a man's ftrength." ' 



He then goes on to confider " more narrowly what a man 

 realli/ does, when he performs what Mr. Smeaton allows to be 

 the produclion of a meafarable mechanical effed. Suppofe a 

 weight of 30 pounds hanging by a cord which pafifes over a 

 pulley, and that a man taking this cord over his flioulder, 

 turns his back to the pulley, and walks away from it, we 

 know that a man of ordinary force will walk along raifing this 

 weight at the rate of about fixty yards in a minute, or a yard 

 in every fecond, and that he can continue to do this for 

 eight or ten hours from day to day, and that this is all he can 

 do without fatigue. Here are 30 pounds raifed uniformly 

 :180 feet in,ia<jpi{nute, and Mr. Smeaton would exprefs this by 

 30 X 180 or 5400, and would call this the meafure of the me- 

 chanical effeci, and alfo of the expenditure of power. This 



.is very different from our meafure 57600." — Yes, but I hope 

 not the lefs conclufive on that account. 



It is wholly incoraprehenfible to me why thofe men (who 

 have certainly a right to controvert any propofition which 

 appears to them erroneous) fhould take up the fubjed, afluming 

 points which the dodrine advanced by Mr. Smeaton has no- 

 thing to do with. It is clear that all this animal exertion 

 comes at laft to the law of bodies falling in accelerated 

 velocity, which Smeaton allows. to be a diftincl confideration, 

 as he fays, ** if the weight defcends quickly, it is fenfibly 



j^^compounded with another law, viz. the law of acceleration 



\py gravity." But how incontiftent is it to go about to eluci- 

 date the laws of bodies in motion by the adion of a man or a 

 horfe. What is the expenditure of animal power but a wade 

 of what has been ufually termed by anatomifts nervous 

 fp.irits, or perhaps an inceptive diforganization of the con- 

 ftituent parts of the ligaments and mufcles ? in tliort, we may 

 compare it to contradions, inflammation, and gangrene, but 

 never to the momentum acquired by a body moving through 



^a certain fpace in a certain time. It is remarkable, that all 

 this reafoning is about that of which Mr, Smeaton has never 



. faid a word, except in his illuilratlon of the mechanic power 



necelTary 



i 



