"The Shammal 45-inch engine was an open-top cylinder, with a chain to the segment-head wooden beam. So was the 63-inch cylinder Stray Park engine, then called Wheal Gons[76] in Dolcoath sett, and the Boulton and Watt 63-inch cylinder double-acting.
"There used to be great talking about different boilers; a boiler of Captain Trevithick's worked with higher steam than the others. Just before Captain Dick came back to the mine a Boulton and Watt hearse boiler had been repaired with a new bottom; it was never used. I and William Causan took a job to cut up the boiler at 1s. 6d. the hundredweight; it weighed 17 tons. Jeffrie and Gribble were the mine engineers; Glanville used to be considered Captain Dick's man in the mine. You could stand upright on the fire-bars in the middle hollow of the hearse boiler, and so you could in the outside brick flues; the middle hollow was like a horse-shoe. When Captain Dick put in his cylindrical boilers he altered the 63-inch single; there was hardly anything of her left but the main wall, with the wood bob and a chain to the piston-rod, and also to the pump-rods. There was an air-pump, and I think a second-hand cylinder was brought, but it was a 63-inch; the old Shammal engine had been altered, too.
"The new boiler put in was about 8 feet in diameter and from 30 to 40 feet long, two round tubes went through it; the fire-place in one end of one tube and in the other end of the other tube; after going through the tubes the draught went into the brick flues under the bottom and sides. When the new engine was put in, Gribble said, ‘Why, these little things will never get steam enough;’ everybody said so.
"In the Boulton and Watt engines we didn't trouble about feed-pumps and gauge-cocks.
"A wire came through a stuffing box in the top of the boiler; a biggish stone in the boiler was fastened to one end of the wire, the other end was fastened to a weighted lever near the water cistern, just above the boiler; when the water got low the stone opened the valve in the water cistern. That was when they were putting in Captain Dick's new cylindrical boilers to the old 63-inch engine. She did so much more work, with less coal, that in a year or so they agreed to throw out Boulton and Watt's engine, and to put in a stronger one that could stand Captain Dick's high steam. Jeffrie and Gribble were the mine engineers that put her up. The 76-inch cylinder came from Wales. The big beam was cast at Perran Foundry in 1815; you can see the name and date upon it now. The boiler and the gear-work were made in the mine. The exhaust-valve is exactly as when it was put in, worked by a rack-and-tooth segment. The equilibrium valve is unchanged, except that the rack is taken out and a link put in.
"The steam-valve was taken out soon after she went to work, and the present double-beat valve was put in; it is the first of the kind I ever saw. Some were made before that time with a small valve on the top of the big one, that opened first, to ease the pressure.
"John West[77] fitted up the valve-gear in the mine with the expansive tappets, the same as when she stopped a month or two ago, and the same as the present new one has.
"Captain Dick's cutting off his strong steam at an early part of the stroke, used to make the steam-valve strike very hard; so the new plan valve, with a double beat, was put in; that must have been about 1816 or 1817; and the valve and expansive horn for working were just exactly like what they have put into the present new engine in 1869. She was the engine that showed them how to fork the water, and burn only half the coal.
"I worked in this mine the old atmospheric engines, and then Boulton and Watt; and then Trevithick's boilers in Boulton and Watt; and then Trevithick's boilers and engine; and now I come every day to the new engine, though I can't do much. They give me 35s. a month; and my name is William Pooly, Dolcoath, 1869."
Three years ago (in 1869), when the writer entered the old engine-house in which Watt's 63-inch cylinder double had been erected in 1780, adjoining the old walls that then enclosed that early Newcomen 45-inch cylinder Carloose engine, re-erected by Trevithick, sen., in 1775 in Bullan Garden portion of Dolcoath, an old man sat near a small window in a recess in the thick wall of the engine-house, within reach of the gear-handles of the Jeffrie and Gribble 76-inch cylinder engine that Trevithick, jun., had erected in 1816 on the foundations of the removed Watt engine; he held in one hand a portion of slate from the roof, and in the other an old pocket-knife, one-half of the blade of which had been broken off, leaving a jagged fracture, with which he made the figures of some calculation on the rude slate; on his nose rested the brass frame of a pair of very ancient spectacles, with horn glasses. He answered the writer's question by, "Yes, I am William Pooly; I worked this engine, and the other engines before it—the great double and the little Shammal working out of the same shaft; and I am seventy-four years of age. The 63 single worked upon a shaft up there; she was called Wheal Gons." That old man, still living, had worked in Dolcoath Mine one of the first steam-engines of Newcomen; the 45-inch, modified by Trevithick, sen.; then the 63-inch double of Watt; and, finally, the high-pressure engines of Trevithick, jun.; he saw the open-top cylinders, atmospheric of Newcomen, in the Shammal 45-inch and Wheal Gons 63-inch, with their wooden beams with segment-headed ends, moving in rivalry with the Watt 63-inch double, with cylinder-cover and parallel motion; he saw the two former engines, as altered by Trevithick, jun., using the higher steam from the globular boiler on which Henry Clark worked in 1799, when "there used to be great talking about different boilers, and a boiler of Captain Trevithick's worked with higher steam than the others; and the waggon boiler of Watt, that had just been repaired, was discarded and cut up;" thus described by Trevithick, "the fire-place is 22 feet from fire-door to fire-door, 9 feet wide, and 7 feet thick in fire,"[78] which he proposed to replace in 1806 by a cylindrical boiler to give steam of 25 lbs. on the inch.