relative to Black, Watt, and Cavendish. Ill 



nitrogen, and afterwards to a mixture of gases, the chief of which 

 was carbonic oxide- -M. Arago will keep you "waiting" long 

 before he rejoins you in the advocacy of any part of the sup- 

 posed claims of your client, or thanks you lor classing him 

 with yourself as still cherishing the conviction that " Mr. 

 Watt had, unknown to Cavendish, anticipated his great disco- 

 very." 



That which renders the self-devotion of this knight-errantry 

 complete, is the singular fact that you are fighting for Watt 

 against himself. I had formerly come to the conclusion that 

 he never thought of claiming the discovery in the sense which 

 you suppose, nor in any other respect than as regards the 

 theory of the extrication of heat and light from the combining 

 gases ; and a circumstance has lately been pointed out to me 

 by a friend, which establishes this conclusion. 



The edition of Robison's Mechanical Philosophy, published 

 by Sir D. Brewster, was revised by W T att himself. In that 

 revision we find him by no means indifferent to his own just 

 fame. Writing to the Editor he says, " I have carefully per- 

 used my late excellent friend Dr. Robison's articles, ' Steam 

 and Steam-Engines/ in the Encyclopaedia Britamiica, and have 

 made remarks upon them in such places, where either from the 

 want of proper information, or from too great a reliance on 

 the powers of his extraordinary memory at a period when it 

 probably had been weakened by a long state of acute pain, 

 and by the remedies to which he was obliged to have recourse, 

 he had been led into mistakes in regard to facts, and also in 

 some places where his deductions have appeared to me to be 

 erroneous. Dr. R. qualifies me as ' the pupil and intimate 

 friend of Dr. Black :' he afterwards, in his dedication to me 

 of Dr. Black's Lectures upon Chemistry, goes the length of 

 supposing me to have professed to owe my improvements upon 

 the steam-engine to the instructions and information I had re- 

 ceived from that gentleman, which was certainly a misappre- 

 hension ; as though I always felt and acknowledged my obliga- 

 tions to him for the information I had received from his con- 

 versation, and particularly for the knowledge of the doctrine 

 of latent heat, I never did nor could consider my improvements 

 as originating in those communications. He is also mistaken 

 in his assertion, p. 8 of the preface to the above work, that I 

 had attended two courses of the Doctor's lectures; for unfor- 

 tunately for me, the necessary avocations of my business pre- 

 vented me from attending his or any other lectures at College." 

 Mr. Watt then quotes from these lectures a passage in which 

 Black is made to say, " My own fortunate observation of 

 what happens in the lormation and condensation of steam, had 



