320 Lord Brougham on the Composition of Water. 



vations and reasonings, but almost the whole of the original letter is pre- 

 served in this, and is distinguished by inverted commas. One of the 

 passages thus marked is that which has the important conclusion above 

 mentioned ; and that letter is stated in the subsequent one to have been 

 communicated to several members of the Roj-al Society at the time of its 

 reaching Dr Priestley, viz. April 1783. 



In Mr Cavendish's paper as at first read, no allusion is to be found to 

 Mr Watt's theory. But in an addition made in Mr Cavendish's own hand, 

 after Mr Watt's paper had been read, there is a reference to that theory 

 (Phil, trans. 1784, p. 140), and Mr Cavendish's reasons are given for not 

 encumbering his theory with that part of Mr Watt's which regards the 

 evolution of latent heat. It is thus left somewhat doubtful, whether Mr 

 Cavendish had ever seen the letter of April 1783, or whether he had only 

 seen the paper (of 26th November 1783) of which that letter formed a 

 part, and which was read 29th April 1784. That the first letter was for 

 some time (two months, as appears from the papers of Mr Watt) in the 

 hands of Sir Joseph Banks and other members of the Society during the 

 preceding spring, is certain, from the statements in the Note to p. 330 ; 

 and that Sir Charles Blagden, the Secretary, should not have seen it seems 

 impossible, for Sir Joseph Banks must have delivered it to him at the time 

 when it was intended to be read at one of the Society's meetings (Phil. 

 Trans, p. 330, Note), and as the letter itself remains among the Society's 

 Records in the same volume with the paper into which the greater part 

 of it was introduced, it must have been in the custody of Sir C. Blagden. 

 It is equally diflacult to suppose, that the person who wrote the remark- 

 able passage already referred to, respecting Mr Cavendish's conclusions 

 having been communicated to Mr Lavoisier in the summer of 1783 (that 

 is, in June), should not have mentioned to Mr Cavendish that Mr Watt 

 had drawn the same conclusion in the spring of 1783 (that is, in April at 

 the latest). For the conclusions are identical, with the single difference, 

 that Mr Cavendish calls dcphlogisticated air, water deprived of its phlo- 

 giston, and Mr Watt says, that water is composed of dcphlogisticated air 

 and phlogiston. 



We may remark, there is the same uncertainty or vagueness introduced 

 into Mr Watt's theory which we before observed in Mr Cavendish's, by 

 the use of the term Phlogiston, without exactly defining it.* Mr Ca- 

 vendish leaves it uncertain, whether or not he meant by Phlogiston sim- 



April 1783, and that to Mr De Luc of 26th November 1783, should be succes- 

 sively read. The former was done on the 22d, and the latter on the 29th April 

 1784. [Note Bv Mr James Watt.] 



" Mr Watt, in a note to his paper of 26th November 1783, p. 331, observes, 

 " previous to Dr Priestley's making these experiments, Mr Kirwan had proved 

 by very ingenious deductions from other facts, that inflammable air was in all 

 probability the real phlogiston in an aerial form. These arguments were per- 

 fectly convincing to me, but it seems proper to rest that part of the argument 

 on direct experiment." [Note bv Mr James Watt.] 



