212 Dr. Henry on the Philosophical Character of Dr. Priestley. 



could such refined investigations have then been carried on 

 with any success, on account of the imperfection of philosophi- 

 cal instruments. It would have been fruitless also at that 

 time to have indulged in speculations respecting the ultimate 

 constitution of bodies; — speculations that have no solid ground- 

 work, except in a class of lacts developed within the last thirty- 

 five years, all tending to establish the laws of combination in 

 definite and in multiple proportions, and to support the still 

 more extensive generalization which has been reared by the 

 genius of Dalton. 



It was, indeed, by the activity of his intellectual faculties, 

 rather than by their reach or vigour, that Dr. Priestley was 

 enabled to render such important services to natural science. 

 We should look in vain in anything that he has achieved, 

 for demonstrations of that powerful and sustained attention, 

 which enables the mind to institute close and accurate com- 

 parisons ; — to trace resemblances that are far from obvious ; — 

 and to discriminate differences that are recondite and obscure. 

 The analogies which caught his observation lay near the sur- 

 face, and were eagerly and hastily jiursued ; often, indeed, 

 beyond the boundaries, within which they ought to have been 

 circumscribed. Quick as his mind was in the perception of 

 resemblances, it appears (probably for that reason) to have 

 been little adapted for those profound and cautious abstrac- 

 tions which supply the only solid foundations of general laws. 

 In sober, patient, and successful induction, Priestley must 

 yield the palm to many others, who, though far less fertile than 

 himself in new and happy combinations of thought, surpassed 

 him in the use of a searching and rigorous logic; in the art 

 of advancing, by secure steps, from phaenomena to general con- 

 clusions; — and again in the employment of general axioms as 

 the instruments of further discoveries. 



Among the defects of his philosophical habits, may be re- 

 marked, that he frequently pursued an object of inquiry too ex- 

 clusively, neglecting others, which were necessai'ily connected 

 with it, and which, if investigated, would have thrown great 

 light on the main research. As an instance, may be mentioned 

 his omitting to examine the relation of gases to water. This 

 relation, of which he had indistinct glimpses, was a source of 

 perpetual embarrassment to him, and led him to imagine 

 changes in the intimate constitution of gases, which were in 

 fact due to nothing more than an interchange of place between 

 the gas in the water and that above the water, or between the 

 former and the external atmosphere. Thus he erroneously 

 supposed that hydrogen gas wtis transmuted into azotic gas, 

 by remaining long confined by the water of a pneumatic cis- 

 tern. 



