M*. GREGORY ON MECHANIC POWER. 15 



for adequate feparate expreffions to denote every idea the 

 mind can form, is to facrifice precifion and accuracy at the 

 ihrine of an ill-judged fuperfluity. The common refemblance 

 between words efteemed fynonimous, does not comprehend 

 the aggregate fignification, but fome ifulated particular aU 

 tendant upon all, in fome fuch manner as may be traced in 

 individuals of the fame fpecies: there is generally one, if not 

 more qualities, on which a manifeft diftinclion depends ; and 

 the determination of fuch qualities is highly deferving the 

 notice, not only of the linguift, but of all who aim at philo- 

 fophical precifion. I have not leifure to look attentively 

 over twenty-five clofely printed quarto pages, in order to find 

 how ProfelTor Robifon diftinguifhes heavinefs from weight. 

 But the labour is unneceiTary ; for the diftinction has often 

 been made; and I will take the liberty of delineating it in the 

 words of an author who is in no danger of having his fenli- 

 ments warped to fquare with the tenets of any fpeculalive 

 mechanical fyliem : I now advert to Dr. Trufler, who in his Trufl-t*s re- 

 work on fynonimous words fpeaks thus :— n&wdnd&hu 



" Heavinefs, weight. — In the figurative fenfe the difference 

 of thefe words is fo extremely great, as needs no pointing 

 out; in the literal indeed, they are offer! confounded: con- 

 fidered then in this laft fenfe, heavinefs is that quality in a 

 body which we feel, and diftinguifti by itfelf : "weight is the 

 meafure and degree of that quality, which we cannot afcertain. 

 but by companion.— We fay abfolutely, and in an undeter* 

 mined fenfe, that a thing is heary ; but relatively, and in a 

 manner determined, that it is of fuch a weight, for example, 

 of two, three, or four pounds. — A thoufand circumftances 

 prove the heavinefs of the air; and the mercury determines 

 its exafi weight." Vol. I. p. 133. 



My letter has attained a much greater magnitude than was 

 at firft intended, and I will now conclude if. The remarks 

 I have been tempted to offer, are founded upon the mod 

 correct interpretation I could put upon Mr. Hornblower's 

 language; and if I have any where mifunderftood his mean- 

 ing, I (hall be pleafed to fee that mifunderftanding candidly 

 removed. I entenain great refpeft for that gentleman's 

 talents a* a practical engineer; though I cannot but think him 

 completely wrong in moft of thofe remarks which have oc- 

 casioned this communication. I have replied to fuch of his 



firi&ures 



