476 JAMES WATT. 



Society, did not see the Memoir. Sir Joseph Banks must have 

 given it to him, since he intended it to be read at the meeting, 

 (Phil. Trans. 1784, p. 330, note.) Let us add that as the letter 

 was preserved in the archives of the Society, it was in charge 

 of Blagden, the Secretary. Would it be possible to sup- 

 pose that the person whose hand wrote the remarkable passage 

 already quoted, relative to a communication made to Lavoisier, 

 in June, 1783, of the conclusions that Cavendish had come to, 

 would not have told Cavendish that Watt had come to those 

 conclusions at the latest in April, 1783 ? The conclusions are 

 identical, with the mere difference that Cavendish calls de- 

 phlogisticated air water deprived of its phlogiston, and that 

 Watt affirms water to be a union of dephlogisticated air and 

 phlogiston. 



We must remark that in Watt's theory there is the same 

 uncertainty, the same vagueness, which we have already ob- 

 served in that of Cavendish, and that it also proceeds from the 

 use of the term phlogiston, which was not well defined.* In 

 Cavendish we cannot decide whether phlogiston is merely in- 

 flammable air, or whether this chemist is not rather inclined 

 to consider a combination of water and phlogiston as inflam- 

 mable air. Watt says expressly, even in his Memoir of the 

 26th November, 1783, and in a passage that does not form 

 part of the April letter in 1783, that inflammable air, accord- 

 ing to his ideas, contains a small quantity of water and a great 

 deal of elementary heat. 



These expressions from two such eminent men, should be 

 regarded as indicating a certain degree of hesitation, relative 

 to the composition of water. If Watt and Cavendish had had 

 a precise idea that water results from the union of two gases 



* In a note to his Memoir of the 26th of November, 1783 (p. 331), 

 we read the following remark by Watt: "Anterior to Dr. Priestley's 

 experiments, Kirwan had proved, by some ingenious deductions bor- 

 rowed from other facts, that inflammable air is in all probability the 

 true phlogiston in an aerial form. Kirwan's arguments appear to me 

 perfectly convincing; but it seems more suitable to establish this point 

 of the question by direct experiments." 



