12 Dr Henry's Estimate of 



in science, either for individuals or for nations, the title to which 

 may be at once set aside by an appeal to public and authentic 

 records. 



It was in England, not in France, that the first decided ad- 

 vances were made in our knowledge of elastic fluids. To say 

 nothing of anterior writers, Dr Black had traced the causticity 

 acquired by alkalies, and by certain earths, to their being freed 

 from combination with fixed air; and Mr Cavendish, in 1T66, 

 had enlarged our knowledge of that gas and of inflammable 

 air. In England, the value of these discoveries was fully ap- 

 preciated ; in France, little or no attention was paid to them, 

 till the philosophers of that country were roused by the striking 

 phenomena exhibited by the experiments of Priestley. Lavoisier, 

 it is true, had been led, by an examination of evidence derived 

 from previous writers, to discard the hypothesis of phlogiston. 

 The discovery of oxygen gas by Dr Priestley not only completed 

 the demonstration of its fallacy, but served as the corner-stone 

 of a more sound and consistent theory. By a series of researches 

 executed at great expense, and with consummate skill, the 

 French philosopher verified in some cases, and corrected in 

 others, the results of his predecessors, and added new and im- 

 portant observations of his own. Upon these united, he 

 founded that beautiful system of general laws, chiefly relating 

 to the absorption of oxygen by combustible bodies, and to the 

 constitution of acids, to which alone the epithet of the Anti- 

 phlogistic or French theory of chemistry is properly applied. 

 Of the genius manifested in the construction of that system, and 

 the taste apparent in its exposition, it is scarcely possible to 

 speak with too much praise. But it is inverting the order of time 

 to assert, that it had any share in giving origin to the researches 

 of Priestley, which were not only anterior to the French theory, 

 but were carried on under the influence of precisely opposite 

 views. This, too, may be asserted of the discoveries of Scheele, 

 who, at the same period with Dr Priestley, was following, in a 

 distant part of Europe, a scarcely less illustrious career. 



It is the natural progress of most generalizations in science, 

 that, at first too hasty and comprehensive, they require to be 

 narrowed as new facts arise. This has happened to the theory 

 of Lavoisier, in consequence of its having been discovered. 



