5^8 WECMANrC rOWER. 



Mcafufcof as it would feem with Mr. Smeaton's meafare, that there is no 

 ^Iffta,^^"^" power expended, no effed produced. On the contrary we 

 know there is a power expended, and that effedl, if fufficiently 

 long continued, would conrjpletely tire the horfe. Then let 

 us have a poji 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 etfed produced ; and I 

 t . beg leave to afk ray opponents, what is the power expended 



when a horfe or other animal is placed there to fuftain the 

 weight ? is it any more than the expence of nervous or 

 mufcular a£iion ; and has that any alialcgy with a weight 

 defcending through a given fpace, either uniformly or ac- 

 celerated ? and, I afk again, what is the effe6l produced more 

 than what is produced by the poft ? the horfe does but keep 

 the weight from dropping into the well, and the poft will do 

 the fame ; indeed you may fay, that when you hang up your 

 hat, that the pin which fuflains it, prevents it from falling, is 

 does the horfe the mafs in the well, and that therefore there 

 mufl be fome power expended on the pin. 



It is really difficult to be grave on this occafion ; but I feel 

 myfelf reflrained by the magnitude of the fubjeft, and its im- 

 portance to the community. Profeffor Robifon fays, when a 

 man holds out his arm horizontally, the exertion towards the 

 end of a quarter of an hour gives the mofl dillrefling fatigue, 

 and then fays this is an expenditure of mechanical power, 

 which I fhall take the liberty to deny for the prefent. But is 

 it fuch a mechanical power as Smeaton's, or in tine, is it a 

 power made up of a mafs of matter moving with any deter- 

 minate velocity either uniform or accelerated? If the learned 

 Profeffor intended to familiarize the dodrine to people of 

 common fenfe, he could not have chofen a more indire<5l and 

 perplexing example. 



But let us attend a little further to the fubje<5l in the fourth 

 feftion of the article Machinery, Sup. Ency. Brit. There he 

 lays, ' that *' when a man fupports a weight for a iingle in- 

 llant, he certainly balances the preffure or a6tion of gravity 

 on that body," by the w^ay here is a great want of precillon 

 in the expreffion, *' preffure oi^ action of gravity" as if they 

 were fynonimous terms, whereas preffure certainly denotes 

 repulfwjZt if the term will bear any definition at all, and to 

 explain the term gravity if it will not admit o( atlraBion, I am 



fiire 



