4 Dr Henry's Estimate of 



be found that is incapable of absorbing or acting upon them*. 

 He obtained, and distinctly described -f, the curious crystalline 

 compound of sulphuric acid with the vapour of nitrous acid, or, 

 more correctly, of sulphuric and hyponitrous acids, which, being 

 of rare occurrence, was forgotten, and has since been redisco- 

 vered, like many other neglected anticipations of the same au- 

 thor. 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 illustrated by sim- 

 ple 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 accelerate 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 mus- 

 cle and tendon ; of the functions and economy of living vegeta- 

 bles ; and of the relations and subserviency which exist between 

 the animal 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 

 divscoveries, of less importance singly, but forming altogether a 

 tribute to science, greatly exceeding, in richness and extent, that 

 of any contemporary, without pronouncing that their author 

 must have been furnished 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 ap- 

 prehension, 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 



• Series i. vol. ii p. 175. t Series ii. vol. i. p. 26. 



