74 On the Refractive Powers — 
focal distances appeared to be as given in the 
following table. 
Liquids See TN toca dist. . haters 
Watery stiscasess pei 1.00 _ ' 8.4 1.00 
Nitrous aaiaderas 1.33 96 adders 
Sulphurie acid tie 170 10.25 132 
This at once shews that the law, noticed 
respecting muriatic acid, does not apply to 
the nitrous or sulphuric, as the specifie gra- 
vity of each is very considerably more than 
in proportion to the focal distance of the lens, 
when containing either: this circumstance 
seems to point out some similitude between 
the constitutions of muriatic acid and of wa- 
ter; the idea once entertained of the consti- 
tuents of both being of the same species (but 
in different proportions), is I believe however 
generally exploded. . 
Dr. Wollaston and others have ascertained 
the refractive powers of some of the acids 
(and other substances), but I am not aware 
that the detail I have ventured upon, regard- 
ing the muriatic acid, &c. has been given be- 
fore: If such is the case, I have only to plead 
ignorance of the fact. 
The ratio which the refractive power of 
