TI1K WATT AND THE TREVITHICK ENGINES. 139 



about the proportions of it ; if they have not, I shall be particu- 

 larly obliged to you to desire them to do so, for by his expe- 

 rience of what he has done they may be benefited, for it would 

 be a shocking thing to have a bad engine put up for the first 

 time in his native county. 



" Mrs. Homfray unites with me in best compliments, and 

 wishing you many happy returns of the season. 



" I remain, dear Sir, 



" Your most obedient servant, 



"SAMUEL HOMFRAY. 



" To Mil. DAVIES GIDDY." 



The evidence in this contest between the Watt low- 

 pressure steam vacuum engine and the Trevithick high- 

 pressure steam-puffer engine is in favour of the new 

 principle ; for the steam-engine with an 18-inch cylinder 

 did fifty per cent, more work than the vacuum engine 

 with a 24-inch cylinder with an equal quantity of coal, 

 though the latter was seventy-five per cent, larger than 

 the former ; and a still greater economy was expected 

 from the larger boiler to be built, 26 feet long, 7 feet 

 in diameter, with internal fire-tube 4 feet 4 inches dia- 

 meter at the fire end, tapering to 21 inches at the 

 chimney end. 



Thus in 1804 the cylindrical boiler in Wales had 

 nearly reached its present form, and Homfray thought 

 that none but idiots would prefer the Watt engine ; 

 forgetting that Trevithick's near friends and neigh- 

 bours were carrying on a similar contest at Dolcoath 

 Mine. 



" PENYDABRAN PLACE, January 2nd, 1805. 



" Mu. DAVIES GIDD?, 



" Dear Sir, I have duly received your favour enclosing 

 a letter for Mr. Trevithick, and which I, according to your 

 desire, forwarded to him at Manchester, where he now is ; and a 



