VARIOUS INVENTIONS. 9 



" This trial of Mr. Sheffield's has put it out of my power to 

 get a patent, and now I do not know how to get paid. 



" I should be content with 5 per cent, on the profits gained 

 by this plan, and would conduct the business for the mines with- 

 out salary. Should you chance to fall on the subject with his 

 Lordship, be pleased to mention something about the mode of 

 my payment, as his Lordship is by far the properest person to 

 begin with about my pay, for after his Lordship has agreed to 

 the sum, and Dolcoath Mine the first to try the experiment, I 

 think all the county will give way to what he might propose. 

 But I wish something to be fixed on before all the agents in the 

 mines know how to be smelters themselves, after which I expect 

 no favour, unless first arranged. 



" I remain, Sir, 



" Your very humble servant, 



" EICHARD TREVITHICK." 



How great was the practical insight his genius gave 

 him, and how imperfectly his followers have acted on 

 this advice given sixty years ago ! 



The chimney that at its top would ignite paper, 

 threw to waste four and a half times more heated air 

 than was requisite to supply the quantity of heat which 

 passed through the working cylinder in steam, and at a 

 temperature nearly four times greater than the tem- 

 perature of the steam. It needs only to observe the 

 burnt appearance of a steamboat funnel of the present 

 day to know how wasteful we still are, or how very 

 ignorant of improved methods of economizing fuel. 



To prevent this waste of heat up the chimney he pro- 

 posed to do away with the chimney altogether; the 

 fire-place was to be a close one, having a blast under 

 the fire-bars of a strength sufficient to force the air, 

 heated by its passage through the fire, direct through 

 a small valve into the water in the boiler, by which 



