210 Dr. Henry 07i the Philosophical Character of Dr. Priestlei^. 



rious crystalline compound of sulphuric acid with the vapour 

 of nitrous acid, or, more correctly, of sulphuric and hyponi- 

 trous acids, wliich beiuy of rare occurrence, was forgotten, and 

 has since been I'ediscovered, likemanyother neglectedanticipa- 

 tions of the same author. He greatly enlarged our knowledge of 

 the important class of metals, and traced out many of their most 

 interesting relations to oxygen and to acids. He unfolded, 

 and illustiated by simple and beautiful experiments, distinct 

 views of combustion ; of the respiration of animals, both of 

 the inferior and higher classes; of the changes produced in 

 organized bodies by putrefaction, and of the causes that acce- 

 lerate or retard that process ; of the importance of azote as the 

 characteristic ingredient of animal substances, obtainable by 

 the action of dilute nitric acid on muscle and tendon; of the 

 functions and ceconomy of living vegetables; and of the rela- 

 tions and subserviency which exist between the animal and 

 vegetable kingdoms. After trying, without effect, a variety of 

 methods, by which he expected to purify air vitiated by the 

 breathing of animals, he discovered that its purity was restored 

 by the growth of living and healthy vegetables, freely exposed 

 to the solar light. 



It is impossible to account for these, and a variety of other 

 discoveries, of less importance singly, but forming altogether 

 a tribute to science, greatly exceeding in richness and extent 

 that of any contemporary, without jironouncing that their 

 author must have been furnished by nature with intellectual 

 powers far surpassing the common average of human endow- 

 ments. If we examine with which of its various faculties the 

 mind of Dr. Priestley was most eminently gifted, it will, I be- 

 lieve, be found that it was most remarkable for clearness and 

 quickness of apprehension, and for rapidity and extent of 

 association. On these qualities were founded that apparently 

 intuitive perception of analogies, and that happy facility of 

 tracing and pursuing them through all their consequences, 

 which led to several of his most brilliant discoveries. Of these 

 analogies many were just and legitimate, and have stood the 

 test of examination by the clearer light, since reflected upon 

 them from the improved condition of science. But, in other 

 cases, his analogies were fanciful and unfounded, and led him 

 far astray from the path which might have conducted him 

 directly to truth. It is curious, however, as he himself observes, 

 that in missing one thing, of which he was in search, he often 

 found another of greater value. In such cases, his vigilance 

 seldom failed to put him in full possession of the treasure upon 

 which he had stumbled. Finding by experience how much 

 chance had to do with the success of his investigations, he re- 

 solved 



