l8b 0« the HyiiraiAiti'^. 



degrees, that is, to 40" or 42^ of the thermometer, and wilt 

 then begin to expand as its heat is auo;mented, at firft flnwly^ 

 and afterwards gradually more rapidly, fo as to obferve upon 

 the whole a very iucreafing prooreflion. 



" Now mixtures of thefe two fubftances will, as may be 

 fuppofed, approach 10 the lefs or the gre;uer of thofe progref- 

 fions, according as they are compounded of more fpirit or 

 more water; whllft their total expanfion will be greater ac- 

 cording as more fpirit enters into their compofilion : but the 

 exaft quantity of the expanfion, as well as the law of the pro- 

 greffion, in all of them, can be determined only by trials. 

 Thefe were therefore the two other principal objedls to be 

 afcertained by experiment.'* Sir Charles then proceeds to 

 defcribe thofe various experiments, and which are too long 

 to admit an infertion of them here ; but from a perufal it will 

 be perceived they were conduced with a degree of patient 

 inquiry, minutenefs of attention, and accuracy of inveftiga- 

 tion, feldom to be met with, and which, with the calcula- 

 tions grounded on them by Mr. Gilpin, clerk of the fociety, 

 and publifhed in the Tranfa<Slions for 1794, have removed 

 ihofc obfcurities with which the fubjeiSl had heretofore been 

 enveloped. 



Thefe celebrated experiments, and the table deduced from 

 them, have been minutely examined by feveral of the ablcft 

 philofophers in Franee and various other parts of the conti- 

 nent, and they are allowed to be what Mr. Nicholfon (who 

 has alfo minutely examined them), in his Chemical Dic- 

 tionary, fays, may be confidered as fundamental refults ; and 

 it is fomewhat remarkable that, fince their publication in 

 1794, no perfon has hitherto availed himfelf of the important 

 information they contain, as a foundation for putting a pe- 

 riod to thofe irregularities and uncertainties which have been 

 fo long and fo univcrfally complained of. 



That hydrometers Ihould be complicated in their flruc- 

 tures, and erroneous in their indications, previous to this 

 period, is not to be wondered at. 



The fpecific gravity of the fpirit, which is the foundation 

 of the hydrometer indication, was but little attended to; and 

 thofe variations which take place in the fpecific gravity, 

 through the le eral caufes above mentioned, having never be- 

 fore that period been precifely afcertained, hydrometers, in- 

 ftead of being graduated by this unerring teft, have been gra- 

 duated by cotnparifon With another inflrument, called a 

 ftandaru, but no means have been pointed out to prove that 

 this ftandard was correc^h 



Thefe tables of Mr. Gilpin, howeverj furniflj fuch elemcn- 

 7 tary 



