396 WATT. 



read, there is a reference to that theory (Phil. Trans. 1784, 

 p. 140), and Mr. Cavendish's reasons are given for not en- 

 cumbering 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 seen only 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 difficult to suppose, that the person 

 who wrote the remarkable passage already referred to, re- 

 specting Mr. Cavendish's conclusions having been communi- 

 cated to M. 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 

 dephlogisticated air, water deprived of its phlogiston, and 

 Mr. Watt says that water is composed of dephlogisticated air 

 and phlogiston. 



We may remark, there is the same uncertainty or vague- 

 ness introduced into Mr. Watt's theory, which we before ob- 

 served in Mr. Cavendish's, by the use of the term Phlogiston, 

 without exactly defining it. Mr. Cavendish leaves it uncer- 

 tain, whether or not he meant by phlogiston simply inflamma- 

 ble air, and he inclines rather to call inflammable air, water 

 united to phlogiston. Mr. Watt says expressly, even in his 

 later paper (of November 1783), and in a passage not to be 

 found in the letter of April 1783, that he thinks that inflam- 



