500 Rev. W. V. Harcourt on Lord Brougham's statements 



buted its elasticity to "the expansion of the fire particles 

 lodged in the minium, supposing fire to be a particular fluid 

 which maintains its own essence and figure, remaining always 

 fire, though not always burning," — or Priestley, who observed 

 that it supported combustion, — or Lavoisier, who distinguished 

 it as a gas, sui generis, and determined its principal com- 

 binations, — if the question be, which of these names deserves 

 the highest place in "the history of this discovery" a philoso- 

 pher I apprehend might be apt to hesitate, — especially perhaps 

 between those which stand first in the list, and that which 

 stands last. 



But you have made a greater mistake in attributing to 

 Priestley the discovery of nitrogen* ; and in that mistake have 

 again wronged Cavendish of his due. Had you taken the 

 trouble to read a paper on this subject which I have published 

 from his MSS.f, you would have found that the same philoso- 

 pher, who exceeded all his cotemporaries in analysing the air 

 with accuracy, was the first who demonstrated it to contain, 

 after burning, a mephitic gas, incapable of supporting com- 

 bustion, and distinct from fixed air: you would have known 

 that, some time before Priestley's publication in the Philosophi- 

 cal Transactions of March 1772, Cavendish communicated to 

 him this paper, containing all the details of an experiment, in 

 which a measured volume of air, confined under water, was 

 passed backwards and forwards through a bent tube filled 

 with powdered charcoal, and heated red-hot — the absorption 

 was found to be definite, and the total loss of volume was 

 ascertained — the fixed air was separated by soap-leys — the 

 volume separated was observed and deducted — the specific 

 gravity of the residual gas was examined, and it was found 

 " rather lighter than common air;" lastly, it was found to 

 extinguish flame, but to extinguish it, by the criterion of the 

 watch, more slowly than fixed air. I know that you would 

 be far from conceding to me that any experiment, however 

 skilfully devised, carries with it its own conclusions : but then 

 you would have known too the very words in which Cavendish 

 conveyed those conclusions to Priestley — " The natural mean- 

 ing of mephitic air is any air which suffocates animals; and 

 this is what Dr. Priestley seems to mean by the word : but in 

 all probability there are many kinds of air which possess this 

 property: I am sure there are two — namely fixed air, and 



* This discovery has been also erroneously assigned to Rutherford, to 

 whom Robison, who derides "the trifling or vague writings of a Nollet, a 

 Ferguson or a Priestley," (Edinburgh Evangel. Physics,) would fain ascribe 

 also a share in the discovery of oxygen. 



f Report of the British Association, Append, to Address, p. 63. 



