Dr. Henry on the Philosophical Character of Hr. Priestley. 2 1 7 



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. Caven- 

 dish, in 1766, had enlarged our knowledge of that gas and 

 of inflammable air. In England, the value of these discoveries 

 was fully appreciated ; in France, little or no attention was 

 paid to them till the philosophers of that country were I'oused 

 by the striking phaenomena exhibited by the experiments of 

 Priestley. Lavoisier, it is true, had been led, by an examina- 

 tion 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 fal- 

 lacy, but served as the coi-ner-stone of a more sound and con- 

 sistent 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 important 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 Antiphlogistic or French 

 theory of chemistry is properly applied. Of the genius mani- 

 fested in the construction of that system, and the taste appa- 

 rent 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 

 Priestle}', 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 fol- 

 lowing 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 

 that combustion is not necessarily accompanied with an ab- 

 sorption of oxygen, and that acids exist independently of 

 oxygen, regarded by him as the general acidifying principle. 

 But after all the deductions that can justly be made on that 

 account from the merits of Lavoisier, he must still hold one 

 of the highest places among those illustrious men who have 

 advanced chemistry to its present rank among the ph3'sical 

 sciences. It is deeply to be lamented that his fame, otiierwise 

 uns^ullied, should have been stained by his want of candoui" 

 and justice to Dr. Priesdey, in appropriating to himself the 

 N.a. Vol. 11. No. G3. ICarch 183'.i. 2 F discovery 



