132 THE WATT AND THE TREVITHICK ENGINES. 



him, for after four or five days Trevithick again 

 wrote : 



" I am sorry to inform you that the experiments that were to 

 be exhibited before the London gents are put off, on account of 

 an accident which happened to Mr. Homfray. I find myself 

 much disappointed on account of the accident, for I was desirous 

 to make the engine go through its different work, that its effect 

 might be published as early as possible." l 



While constructing those numerous high- pressure 

 engines for rolling mills, winding engines, and pumping 

 engines, the Welsh and Newcastle locomotives were 

 being made and worked, yet he found time to teach the 

 people of Stourbridge. 



" MR. GlDDY, " STOURBRIDGE, July 5th, 1804. 



" Sir, I should have answered your letter some time 

 since, but waited to set two other engines to work first. The 

 great engine at Penydarran goes on exceedingly well. The 

 engine will roll 150 tons of iron a week with 18 tons of coal. 

 The two engines of Boulton's at Dowlais burn 40 tons to roll 

 160 tons ; they are a 24-inch and a 27-inch double. The engine 

 at Penydarran is 18-J- inches, 6-feet stroke, works about eighteen 

 strokes per minute : it requires the steam about 45 Ibs. to the 

 inch above the atmosphere. I worked it expansive first, when 

 working the hammer, which was a more regular load than roll- 

 ing ; then with steam high enough to work twelve strokes per 

 minute with the cock open all the stroke ; then I shut it off at 

 half the stroke, which reduced the number of strokes to ten 

 and a half per minute, the steam and load the same in both ; 

 but I did not continue to work it expansively, because the work 

 in rolling is very uneven, and the careless workmen would 

 stop the engine when working expansive. 



" When the cylinder was full of steam the rollers could not 

 stop it ; and as coal is not an object here, Mr. Homfray wished 



1 See Trevithick's letter, 9th March, 1804, vol. i., p. 168. 



