Biographical Memoir of Henry Cavendish. 213 



suits, and the importance of his discoveries was soon evinced by 

 their fecundity. The fact once ascertained, that there might 

 exist various elastic fluids, constant in their properties and spe- 

 cifically different in their nature, first gave rise to Priestley's re- 

 searches, which led to the discovery of two new kinds of those 

 fluids, the phlogisticated and nitrous airs. It was then begun 

 to be seen how far the different kinds of air might exercise 

 their influence upon the phenomena of nature, and how little 

 solidity systems of physics and of chemistry could have, which 

 were formed without any regard to agents so powerful and uni- 

 versal. The intellectual faculties agitated by that impatience 

 of doubt which forms their chief spring, entered into a sort of 

 fermentation, and each endeavoured to supply what he saw to be 

 wanting in these theories. Bergman's introduction of fixed air 

 among the acids, while it simplified chemistry a little, formed 

 but a slight palliative to the radical defect which had been per- 

 ceived in it. This state of things had existed for seven years, when 

 Lavoisier was struck as with the first dawn of his famous theory. 

 Finding a great quantity of fixed air evolved during the reduc- 

 tion of the metals by charcoal, he concluded that the calcina- 

 tion of these substances was nothing but their combination with 

 fixed air. A year after, Bayen reduced calxes of mercury with- 

 out cliarcoal in close vessels, and sapped the chief foundation of 

 the phlogistic theory. Lavoisier then examined the air pro- 

 duced by these reductions without charcoal, and found it re- 

 spirable ; and, about the same time, Priestley discovered that it 

 was precisely the part of the atmosphere necessary at once for 

 respiration and combustion. It was then that Lavoisier made a 

 second step. Respiration, the calcination of metals and combus- 

 tion, said he, are similar operations, combinations of. respirable 

 air; fixed air is the peculiar produce of the combustion of 

 charcoal. 



But the phenomena of solutions, the inflammable air which 

 manifests itself in them, were not yet explained. Other six 

 years were required for the accomplishment of this, and it was 

 Mr Cavendish for whom the honour was reserved. 



Scheele had observed that, in burning inflammable air, neither 

 fixed nor phlogisticated air was obtained ; all seemed to disap- 

 pear. Macquer, while trying to arrest the vapour arising from 



