14 MR. GREGORY ON MECHANIC POWER. 



quickly it is fenfibly compounded with another law, viz. the 

 acceleration of gravity. •' Or, adopting other language of 

 Mr. Smealon, he might reftrict his meafures to " the height 

 through which a body Jlowly and equally defcended, or to 

 which it was raifed." But if, inftead of the body's amend- 

 ing or descending flowly and equally, it moved rapidly and* 

 irregularly; or, if the motion was reciprocating, the velocity 

 increafing from quiefcence to a certain magnitude, and 

 tiiminifhing to quiefcence again ; or, if we refer to the re- 

 tarded rife and accelerated fall of heavy {tampers ; in fuch 

 cafe* if Smeaton's meafure be applicable, I with to fee its 

 manner of application explained ; and if it be not univerfally ap- 

 plicable, a point which is, in reality conceded both by Mr. H. 

 and Mr. Smeaton, there is then as to this head no ground of 

 difference between us, and Mr. H's laft letter becomes in a 

 great meafure a fuperfluous labour ; for, admitting the want 

 of univerfality in the rule, is admitting all that I affirmed. 

 Had not the meafure been often very injudicioufly exhibited 

 as univerfal, a thing which Mr. Smeaton himfelf certainly 

 never intended, I mould not have at all referred to it in my 

 former paper. 

 In corr»fl i?a- ft ma . De deemed a flight deviation from the immediate 



jcunee V3tx?ht 



and beevintfs object of this letter, but I truft a juftifiable one, if I briefly 

 ought to be dif- notice the furprize exprefied by Mr. H. on account of Profeflbr 

 &a ' c Robifon's diftinguifhing between weight and heavinefs. 



That the three terms gravity, weight, and heavinefs, admit of 

 a palpable and obvious diftinction, is, in my opinion, in- 

 dubitable: and till this time, I imagined it was univerfally 

 reckoned one great excellence of an accurate philofophica! 

 difquifition, that it comprifed a careful difcrimination of the 

 various acceptations of thefe and other terms, which were 

 commonly reputed fynonimous. There may, undoubtedly, 

 be occafions in which a cautious (election from words of nearly 

 iimilar import may he difpenfed with : but there are many 

 more, particularly when handling philofophical topics, where 

 this careful choice cannot be fafely neglected. And an at- 

 tention to ihis point appears the more neeeflary, when it is 

 recollected, that greater part of the controverfies which 

 have been agitated by men of fcience, have been rather 

 verbal, than relative to thing* in themfelves, To contend for 

 the ule of many terms to exprefs one idea,, inftead of feeking 



for 



