186 OF THE PRESSURE OF UNMIXABLE FLUIDS OF DIFFERENT DENSITIES 



BEz=720' 19" - - - nat. vers. .69106, 

 BC 27 59' 41" - - - nat. vers. .11700, 

 B G = 22 0' 19" - - - nat. vers. = .07285 ; 



consequently, by subtraction, we obtain 

 FH = BF BH ; that is, FIX = .69106 .07285 .61821 , 



and after the same manner, we get 



DH = BD BH; that is, DH .11700 .07285 = .04415 ; 



therefore, according to the proposition, we have 



.04415 : .61821 : : 1 : 14 very nearly. 



196. The above result has been obtained on the supposition, that 

 the fluids enclosed in the tube are mercury and water ; mercury, on 

 account of ,its great density and high degree of purity, is very fre- 

 quently enclosed in tubes and applied to permanent purposes ; but 

 water, by reason of its liability to become putrid, is not so well 

 adapted for the occasion, and consequently, is seldom or never em- 

 ployed in the construction of philosophical instruments. 



197. There are however, several other fluids that do not partake 

 of the putrescent nature of water, and whose specific gravities may be 

 either greater or less according to the required circumstances ; some 

 of these, on account of the colouring matter which they contain, are 

 very convenient, and from the length of time that they retain their 

 spirit and purity, are generally employed in preference to others, which 

 do not possess these very requisite and important characteristics. 



198. Now, the result of our investigation, as we have already 

 observed, is only applicable in the case of mercury and water ; at 

 least, equation (141) implies, that the specific gravity of one of the 

 fluids is expressed by unity, and this, according to our present 

 standard, can only obtain when water becomes the subject of 

 reference. 



199. It is therefore necessary, in order that our formula may apply 

 to fluids without distinction, to bring it into a general form, and this is 

 very easily done; for we have shown in the preceding investigation, that 



but it has also been shown, that 

 d vers. (20 x) vers. (0 a:) ; 



consequently, by comparison, we obtain 



$s' 



vers. (20 a:) vers.(0 a-) ; 



