In 1795 he erected at Wheal Treasury, when his pay was 3s. 6d. a day, his double-acting steam-engine--a model of which is still, I believe, in operation at Battersea--and in 1796 or 1797, he removed to Ding Dong Mine, near Penzance. It was about this time that he, fortunately for himself, met with Davies Gilbert, of Tredrea, afterwards President of the Royal Society, whose impressions of Trevithick are recorded in the following letter to J. S. Enys, Esq., of Enys: 'Eastbourne, April 29, 1839. 'MY DEAR SIR, 'I will give as good an account as I can of Richard Trevithick. His father was the chief manager in Dolcoath Mine, and he bore the reputation of being the best informed and most skilful captain in all western mines; for as broad a line of distinction was then made between the _Eastern_ and _Western_ mines (the Gwennap and the Camborne Mines) as between those of different nations. 'I knew the father very well, and about the year 1796 I remember hearing from Mr. Jonathan Hornblower, that a tall and strong young man had made his appearance among engineers, and that on more than one occasion he had threatened some people who had contradicted him to throw them into the engine-shaft. In the latter part of November of that year I was called to London as a witness in a steam-engine case between Messrs. Boulton and Watt and Maberley. Then I believe that I first saw Mr. Richard Trevithick, Jun., and certainly there I first became acquainted with him. Our correspondence commenced soon afterwards, and he was very frequently in the habit of calling at Tredrea to ask my opinion on various projects that occurred to his mind--some of them very ingenious, and others so wild as not to rest on any foundation at all. I cannot trace the succession in point of time. 'On one occasion Trevithick came to me and inquired with great eagerness as to what I apprehended would be the loss of power in working an engine by the force of steam raised to the pressure of several atmospheres; but instead of condensing, to let the steam escape. I, of course, answered at once that the loss of power would be one atmosphere, diminished power by the saving of an air-pump with its friction, and in many cases with the raising of condensing water. I never saw a man more delighted; and I believe that within a month several puffers were in actual work. 'DAVIES GILBERT.'