1 ] 2 Rev. W. V. Harcourt on Lord Brougham's statements 



suggested to my friend Mr. Watt his improvements in the 

 steam-engine," and remarks, " it is very painful to me to con- 

 trovert any assertion or opinion of my revered friend ; yet in 

 the present case I find it necessary to say that he appears to 

 have fallen into an error*." 



But in revising the article on Steam, and making remarks 

 on those places in which Dr. Robison had been led into mis- 

 takes, Watt makes no remark on the following very decisive 

 passage: — "We know that in vital or atmospheric air there is 

 not only a prodigious quantity of fire which is not in the vapour 

 of water, but that it also contains light, or the cause of light, in a 

 combined state. This is fully evinced by the great discovery of' 

 Mr. Cavendish of the composition of water: there we are taught 

 that water, and consequently its vapour, consists of air from 

 which the light and greatest part of the fire have been sepa- 

 rated ; and the subsequent discoveries of the celebrated Lavoi- 

 sier show that almost all the condensable gases with which we 

 are acquainted, consist either of airs which have lost much of 

 their fire, and perhaps light too, or of matters in which we have 

 no evidence of light and fire being combined in this manner." 



Thus you see, that jealous as Watt appears of any undue 

 share in his own discoveries being attributed even to his 

 " revered friend" Dr. Black, he allows " the great discovery of 

 the composition of water" to be assigned to Cavendish without 

 reclaiming the least participation in it for himself. 



These extracts entirely relieve his memory from any sus- 

 picion of his having been a party to the erroneous statements 

 contained either in the article 'Water' in the first edition of the 

 Encyclopaedia Britannica^to which you have referred, or in the 

 posthumous lectures of Black. Nor do I hold Black responsible 

 for the fabulous history of this discovery given in the latter 

 work. It is well known that that unambitious man left behind 

 him no MSS. of any account, and that the Lectures published 

 under his name were chiefly composed out of the reminis- 

 cences of the able but incorrect Editor. Robison, on historical 

 points, was a very inaccurate writer ; and to his inaccuracy I 

 attribute the extraordinary string of errors on this subject 

 which I have formerly pointed out. 



It is from the latter work that you seem to have taken your 



* I conceive Watt to mean that the facts known to him respecting the 

 condensation of steam, independent of Black's theoretical explanation of 

 them, were the foundation of his improvements ; and I am bound there- 

 fore, on his own showing, to allow that M. Arago has done right in not 

 placing the merit of Watt in the study and application of abstract philo- 

 sophical principles, so much as in ingenuity of mechanical contrivance and 

 the happy adaptation of well-observed facts. 



