LORD BROUGHAM S APPENDIX. 475 



periments. In short, the letter was not read till April, 1 784.* 

 This letter was incorporated by Watt in a Memoir addressed 

 to Deluc, dated 26th Nov. 1783.f Many new observations, 

 and new reasonings, were introduced into this Memoir, although 

 nearly the whole of the original letter was preserved in it, and 

 in the printing it was distinguished from the additions by in 

 verted commas. The important deduction, previously quoted, 

 will be found in the part thus marked. We read also that the 

 letter was communicated to several Fellows of the Royal Soci 

 ety when it reached Priestley in April, 1 783. 



In Cavendish s Memoir, such as it was when read, there was 

 no allusion to Watt s theory ; but it is mentioned in an addi 

 tion, entirely in the handwriting of Cavendish, posterior to the 

 reading of Watt s letters, (Phil. Trans. 1784, p. 140.) In this 

 addition Cavendish gives his reasons for not liking to render 

 his conclusions complicated as Watt did, with considerations 

 relative to the disengagement of latent heat ; but it leaves us 

 in doubt on the question as to whether the author was ever 

 aware of the letter to Priestley of April, 1783, or whether he 

 only saw the letter dated 26th of November, 1783, and read 

 the 29th of April, 1 784 ; on which it is requisite to remark 

 that the two letters appeared in the Philosophical Transactions 

 united in one. The letter to Priestley of the 26th April, 

 1 783, remained some time (two months according to Watt s 

 Memoir,) in the hands of Sir Joseph Banks and other Fellows 

 of the Royal Society, during the spring of 1783. This is what 

 we learn from the circumstances related in the note at p. 330. 

 It seemed difficult to suppose that Blagden, Secretary of the 



* The letter to Priestley was read the 22d of April, 1784. 



t Undoubtedly the Genevese physicist, then in London, received it 

 at the time. It remained in his hands until Watt heard of the reading 

 of Cavendish s Memoir at the Royal Society. From that moment my 

 father made all possible arrangements for the Memoir addressed to 

 Deluc and the letter of the 26th of April, 1783, addressed to Dr. Priest 

 ley, being read immediately at the Royal Society. This reading, 

 claimed by Watt for the Memoir addressed to Deluc, was dated 29th 

 of April, 1784. (Note by Mr. Watt, jun.) 



