| £ | s. | |
| Original cost of the steam-engine | 80 | 0 |
| Building material and rope | 10 | 0 |
| 90 | 0 | |
| Interest on the above 90l. at 5 per cent. | 4 | 10 |
| Wear and tear at 5 per cent. | 4 | 10 |
| 9 | 0 | |
| Original cost of horse machinery for four horses | 60 | 0 |
| Interest on the above at 5 per cent. | 3 | 0 |
| Wear and tear at 15 per cent. | 9 | 0 |
| 12 | 0 |
"Two bushels or 164 lbs. of coal will do the work of four horses, costing 2s. 6d.
"Four horses at 5s. each, gives 20s. Cost of coal, 2s. 6d. as compared with 20s. for horses.
"I remain, Sir,
"Your obedient servant,
"Richard. Trevithick.
"Cornwall, February 20th, 1812.
"Having been requested to witness and report on the effect of steam applied to work a mill for thrashing corn at Trewithen, we hereby certify that a fire was lighted under the boiler of the engine five minutes after eight o'clock, and at twenty-five minutes after nine the thrashing mill began to work, in which time 1 bushel of coal was consumed. That from the time the mill began to work to two minutes after two o'clock, being four hours and three-quarters, 1500 sheaves of barley were thrashed clean, and 1 bushel of coal more was consumed. We think there was sufficient steam remaining in the boiler to have thrashed from 50 to 100 sheaves more barley, and the water in the boiler was by no means exhausted. We had the satisfaction to observe that a common labourer regulated the thrashing mill, and in a moment of time made it go faster, slower, or entirely to cease working. We approve of the steadiness and the velocity with which the machine worked; and in every respect we prefer the power of steam, as here applied, to that of horses.
(Signed) "Matthew Roberts, Lamellyn.
"Thomas Nankivill, Golden.
"Matthew Doble, Barthlever."
This first high-pressure steam thrashing machine was working on the 13th February, 1812, at Trewithen, the property of Sir Christopher Hawkins, as proved by Trevithick's drawing of the machine, his account of the work performed, and the report of the three wise men that the power of steam was preferable to the power of horses. Its first cost was less than that of a horse machine; but to make the calculated amounts come right Trevithick charged 15 per cent. for wear and tear on the horse machinery, and but 5 per cent. on the steam-engine; overlooking the cost of the horses, which would have made the outlay for the horses and machinery greater than for the steam-engine.
The whole design evidences simplicity and consequent cheapness; no complication of valves or valve-gear, no cylinder cover, parallel motion, guide-rods, or air-pump, with its condenser and injection-water.