MECHAKIC POWER. ^SS^ \ 



milTed until It has pafled the unanimous aOent of both theoretic Meafure of 

 and prad^ical mechanics; and I muft here exprefs niy acknow-^'^^^J^^ powcr^ 

 ledgments to Mr. Gregory for his improved method of decid- 

 ing the quertion. It isof abfolute importance, that the draught 

 be in a circular dire<51ion, and alfo that the radius of tire circle 

 be given ; for no polition was ever more demonfirable than 

 that the lefs the radius the lefs can a horfe (whole fides are 

 equal) exert his faculty of tra6tion. 



ButJ muft beg leave to ufea little freedom (in no wife un- 

 becoming, I hope,) in adverting to what Mr. Gregory in 

 conjunflion with ProfelTor Robifon has advanced on the fub- 

 je6l of Mr. Smeaton's mode of defining mechanic poivers and 

 mechanical effeti ; and I am furprifed that among men of talent 

 and atfiduity there can be a difference of opinion. It feems 

 to me, that if any reafon can be found, it mufi be that we do 

 not underftand the fubjed, and, perhaps I may give a decided 

 proof of it in what I (hall advance concerning it. 



However, I am fure that when a ball of caft iron, of twenty^ 

 inches diameter is elevated by means of a pinion and wheel 

 connected to the fides of a pair of flieers, and left to hang 

 there a little while, — if I cut the rope that fufiains it, it will 

 fall freely a certain height, in a certain portion of time, and 

 would dafli a faulty cylinder of a fteam engine in pieces. 

 And I am fo well fatisfied that there was a certain tendency 

 in this ball to fall towards the centre of the earth, that I need 

 not take a moment to examine the truth of it; but that the 

 deftru6lion of the cylinder was occafioned by the ball falling 

 from the point to which it was raifed, (how it was raifed is no 

 part of the fubje6l.) Then I fay, that if the ball had not 

 fallen from the height it was, or if the ball had not been fo 

 heavy as it was, or if it had had its velocity retarded by any 

 ' means, the cylinder would not have been broken. I will 

 add, that had this ball been a true fphere, and the cylinder 

 had not been there, but a certain carved furface in its place, 

 which ftiould have received the ball to prevent it impinging 

 in the line of defcent, it would have been turned out of its 

 courfe conformably to the nature and pofition of the curve : 

 and all that is above common apprehenfion in this matter, fs, 

 that while the ball was falling, its veiocily was increafing 

 every inftant, and that when it met vi4th the curve (if it gave 

 \i an horizontal cowrfe-) it would proceed with uniform velocity 



