AND sntFACK CnNDKNSMK. 327 



The writer's note-book used during those experiments 

 is in his possession, as well as Trevithick's note-book 

 giving particulars of experiments at several mines, from 

 which the following extracts are taken : 



" CORNWALL, August, 1828. Wheal Towan 80-inch cylinder, 

 10-feet stroke, 6*9 strokes per minute, loaded to 9*5 Ibs. on 

 the inch of the piston, with three of Trevithick's boilers, each 

 37 feet long, 6 feet 2 inches diameter, with fire-tube 3 feet 

 9 inches diameter, fire-place 6 feet long, evaporated 13 square 

 feet of water with 1 bushel of coal, 1 duty 87 millions. The 

 heat in the stack was just the same as the heat of the steam 

 in the boiler. Another engine of the same size on the same 

 mine, with similar boilers, but working only 4 06 strokes per 

 minute, loaded to 4*55 Ibs. on each inch of the piston, did 

 50 ' 8 millions. 



" Wheal Vor 53-inch cylinder, 9-feet stroke, 6*59 strokes per 

 minute, loaded to 19*58 Ibs. on each square inch of the piston, 

 did 36 6 millions. 



" Wheal Damsel 41-inch cylinder, 7 feet 6 inch stroke, 

 5 52 strokes per minute, loaded to 21*5 Ibs. on the inch of the 

 piston, did 33 millions. 



" It would appear, therefore, that about 10 Ibs. to the inch on 

 the piston allows of the best duty, and that a 10-feet stroke 

 exceeds in duty a 7 feet 6 inch stroke. 



" The W T heal Towan engine, doing 87 millions, had 1248 feet 

 of tube fire-surface, and a similar amount of external boiler 

 surface in the flues. 2J bushels of coal were consumed each 

 hour, giving about 1000 feet of fire-sides for each bushel of 

 coal consumed per hour, and 50 feet of fire-bars. Those boilers 

 were intended to supply steam for working the engine at ten 

 strokes a minute ; a bushel of coal an hour would in that case 

 have had 600 feet of boiler fire-surface. 



" Binner Downs 70-inch cylinder, 10-feet stroke, did 41 mil- 

 lions. A fire was then put around the cylinder and steam-pipes, 

 which burnt 5 bushels of coal in twenty-four hours, by which 

 the duty was increased to 63 millions. The surface sides of the 



1 84 Ibs. 



