754 Report on the Exhibition of Impiements, 
the steam-cock by means of a hand-screw. The connecting-rod is coupled 
direct to the hemp-packed piston. Such is a brief description of what was 
probably the first high-pressure engine ever used for agricultural work. The 
rim of the fly wheel was grooved, and carried a rope by which the thrashing 
machine was driven. 
The following letter was found after Trevithick's death in an 
old memorandum account-book : it refers in all probability to the 
engine shown at Kilbum: — 
Havle Foundry, Febmary 13th, 1812, 
To Sir Cheistophee Hawkins, Baronet. 
Sir, — I now send you, agreeable to yonr request, a plan and description of 
my patent steam engine which I lately erected on your farm for working a 
thrashing miU. The steam engine is equal in power to four horses, having a 
cylinder 9 in. in diameter. The cylinder, with a moderate heat in the boiler, 
makes 30 strokes in a minute, and as many revolutions of the fly-wheel, to 
every one of which the drum of the thrashing mill, which is 3 ft. in diameter, 
is turned twelve times. The boiler evaporates nine gallons of water in an 
hour, and works sis hours without being replenished. The engine requires 
only little attention — a common labouring man easily regulates it. The 
expense of your engine of 4-horse power compared with the expense of four 
horses is as follows : — 
£ s. d. 
Original cost of steam engine 80 0 0 
Building material and rope 10 0 0 
£90 0 0 
Interest on the above, at 5 per cent 4 10 0 
"Wear and tear, at 5 per cent 4 10 0 
£9 0 0 
Original cost of horse machinery for four horses . . 60 0 0 
Interest on the above, at 5 per cent 3 0 0 
Wear and tear, at 15 per cent 9 0 0 
£12 0 0 
Two bushels, or 164 lb. of coal will do the work of four horses, costii^ 2s. dd. 
Four horses, at 5s. each, gives 20s. Cost of coal, 2s. Qd. as compared with 
20s. for horses. 
I remain. Sir, 
Your obedient servant, 
ElCHARD TeEVTTHICK. 
I am indebted for this letter, as well as for much of the 
description, to the excellent article in the ' Engineer ' of June 
20, 1879, in which the writer proceeds to question the accuracy 
of Trevithick's statement, that the boiler evaporates only 9 gal- 
lons per hour, and works six hours without being replenished, 
