VARIOUS INVENTIONS. 21 



" Query 12th. A governor will be required ; perhaps as good 

 a place MS any for it, out of the way, will be on the cast iron 

 that carries the beam ; you may turn the fly-wheel whichever 

 \\ay you please. If this engine is worked with steam of 25 Ibs. 

 to the inch above the atmosphere, and the steam shut off at 

 one-twentieth part of the ascending stroke of the piston, the 

 power will be as three is to two of Boulton and Watt's single 

 engines. 



" Only two pairs of stones for the present, but calculate 

 those stones to stand in such a way that another pair may 

 be placed, on a future day, if wanted. I have not seen Mr. 

 Kichards lately. I wish you to write a form of an order, in 

 your next, such as you wish, and 1 will get him to write to you 

 accordingly. Put the engine and drum for Lord de Dunstanville 

 out of hand neat and well, as it will be well paid for ; and 

 make the stands, &c., in your own way. 



" KD. TREVITHICK." 



Mr. Richards' flour-mill engine may claim to be the 

 first practical smoke-burner : keeping the fire much 

 thinner at the inner end of the grate-bars than at the 

 fire-door end of the grate, allowed of the freer passage 

 of air through the thinner layer of coal, near the fire- 

 bridge, causing the combustion of the passing gas. 

 This idea has, since the date of Trevithick's letter, led 

 to several smoke-burning patents. The boiler fire-tube 

 was oval, 2 feet 9 inches by 1 foot 11 inches. The 

 open-topped cylinder was supplied with a heavy and 

 deep piston serving as a counterweight, and also as a 

 guide in the cylinder for correcting the angle of the 

 connecting rod. Experience had taught him that the 

 cold sides of the condenser were sufficient to work an 

 engine a great many strokes without a supply of injec- 

 tion ; and he had already used high-pressure steam of 

 25 Ibs. to the inch above the atmosphere, cut off from 

 the cylinder when the piston had performed one quarter 



