4 



Philosophical Character afDr. Priestley. 31 



i 



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quite aware that those acids are essentially gaseous substances, and 

 that they might be exhibited as such, provided a fluid could be found 

 that is incapable of absorbing or acting upon them.* He obtained, 

 and distinctly described,*)- the curious crystalline compound of sul- 

 phuric acid with the vapor of nitrous acid, or, more correctly, of sul- 

 phuric and hyponitrous acids, which, being of rare occurrence, was 

 forgotten, and, has since been rediscovered, like many other neg- 

 lected anticipations of the same author. He greatly enlarged our 

 knowledge of the important class of metals, and traced out of their 

 most interesting relations to oxygen and to acids. He unfolded, and 

 illustrated by simple and beautiful experiments, distinct views of com- 

 bustion ; of the respiration of animals, both of the inferior and higher 

 classes ; of the changes produced in organized bodies by putrefac- 

 tion, and of the causes, that accelerate or retard that process ; of the 

 importance of azote as the characteristic ingredient of animal substan- 

 ces, obtainable by the action of dilute nitric acid on muscle and ten- 

 don ; of the functions and economy of living vegetables ; and of the 

 relations and subserviency, which exist between the animal and veg- 

 etable kingdoms. After trying, without effect, a variety of methods, 

 by which he expected to purify air vitiated by the breathing of ani- 

 mals, he discovered that its purity was restored by the growth of liv- 

 ing and healthy vegetables, freely exposed to the solar light. 



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

 eries, of less importance singly, but forming altogether a tribute to 

 science, greatly exceeding, in richness and extent, that of any con- 

 temporary, without pronouncing that their author must have been fur- 

 nished by nature with intellectual powers, far surpassing the common 

 average of human endowments. If we examine, with which of its 

 various faculties the mind of Dr. Priestley was most eminently gifted, 

 it will, I believe, be found that it was most remarkable for clearness 

 and quickness of apprehension, and for rapidity and extent of asso- 

 ciation. On these qualities were founded that apparently intuitive 

 perception of analogies, and that happy facility of tracing and pursu- 

 ing 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 sci- 



Series L Vol. ii. p. 175. ' t Series II. Vol. i. p. 26. 



