THE WATT AND THE TREVITHfCK ENGINES. 143 



not above 4 Ibs. to the inch ; mine was near 40 Ibs. to the inch ; 

 yet I raised my steam of near 40 Ibs. with a third of the coals 

 by which they got theirs of 4 Ibs. to the inch. This is what I 

 cannot account for, unless it is by getting the fire very small and 

 extremely hot. Another advantage I have is, that there is no 

 smoke that goes off from my fire to clog the fire sides of the 

 boiler, while the common boilers get soot half an inch thick, and 

 the mud falls on the bottom of the boiler, where the fire ought 

 to act ; but in these new boilers the mud falls to the bottom, 

 where there is no fire, and both the inside and outside of the 

 tube are clean and exposed both to fire and water. This fire- 

 place of 14 inches was 5 feet long when I came down, and then 

 the coal did not do above one-seventh of the duty that it now 

 does. 



" I would be very much obliged to you for your opinion on 

 what I have stated, and what advantage you think the greed 

 engine is likely to get from working with steam about 25 Ibs. to 

 the inch, and shut off early in the stroke, so as to have the steam 

 about 4 Ibs. to the inch when the piston is at the bottom. I think 

 this, with the advantage of the fire-place, will make a great 

 saving. 



" The present fire-place is 22 feet from fire-door to fire-door, 

 9 feet wide, and 7 feet thick in fire. There is not one-tenth of the 

 coals that are in the fire-place on fire at the same time ; it will 

 hold 30 tons of coals at one time, and I think that a great deal 

 of coal is destroyed by a partial heat before it takes fire. A 

 boiler on the new plan will not cost more than two-thirds of the 

 old way, and will last double the time, and can be cleaned in 

 three hours. It requires twenty-four hours in the old way, and 

 we need to clean the boilers only one-fourth the number of 

 times. 



" Though these trials have shown so fairly that it is a great 

 advantage, my old acquaintances are still striving with all their 

 might to destroy the use of it ; but facts will soon silence 

 them. 



" I am about to enter into a contract with the Trinity Board 

 for lifting up the ballast out of the bottom of the Thames for all 

 the shipping. The first quantity stated was 300,000 tons per 



