the PUlosopMcal Character of Br Priestley. 7 



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 phenomena to general conclusions ; — and again in 

 the employment of general axioms as the instruments of farther 

 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 necessarily 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 chang- 

 es 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 was transmuted into azotic gas, by remain- 

 ing long confined by the water of a pneumatic cistern. The 

 same eager direction of his mind to a single object, caused him 

 also to overlook several new substances, which he must ne- 

 cessarily have obtained, and which, by a more watchful care, he 

 might have secured and identified. At a very early period of 

 his inquiries, (viz. before November 1771), he was in possession 

 of oxygen gas from saltpetre, and had remarked its striking ef- 

 fect on the flame of a candle ; but he pursued the subject no 

 farther until August 1774, when he again procured the same 

 kind of gas from the red oxide of mercury, and, in a less pure 

 state, from red lead. Placed thus a second time within his 

 grasp, he did not omit to make prize of this, his greatest, dis- 

 covery. He must, also, have obtained chlorine by the solution 

 of manganese in spirit of salt ; but it escaped his notice, because, 

 being received over mercury, the gas was instantly absorbed*. 

 If he had employed a bladder, as Scheele afterwards did, to 

 collect the produce of the same materials, he could not have 

 failed to anticipate the Swedish philosopher, in a discovery not 

 less important than that of oxygen gas. Carbonic oxide early 

 • Series ii. p. 253. 



