It had been and still is the custom to bore rock either with a long and heavy jumper-chisel, lifted a foot or two, and falling by its own weight, pounding to powder a portion of the rock, or by the use of a much smaller chisel called a borer, struck by a hammer. Trevithick having made his steam-engine perform those jumper and borer movements, turned his attention to the improvement of the borer, and found that a revolving bit was more suitable for drilling limestone than the borer-chisel. The powdered stone was removed from the hole by giving a screw form to the stem of the bit. Many years afterwards precisely similar bits for boring wood were patented as new things, and are still used. Within five months of his first communication with the contractors for the Plymouth Breakwater he had designed and made an engine to bore, lift, and convey to the ship's hold 50 tons of stone daily at less than half the cost Rennie was then paying for it.
[Rough draft.]
"Sir,
"Camborne, February 4th, 1813.
"I have your letter of the 31st January requesting to know the time in which the engine will be ready for the bridge at Exeter, and also about giving an additional power to it.
"The engine shall be ready in six weeks from the end of January, and shall be capable of lifting the 10-inch bucket you have ordered instead of the 9-inch before proposed, which was to have delivered 500 gallons of water 12 feet high per minute; but now the engine shall be made to lift in the same proportion as a 9-inch is to a 10-inch bucket, which will be 617 gallons of water per minute instead of 500 gallons, as was before agreed on, and I shall charge you accordingly. I observe that you have ordered the pump, and from the description you give of it, I think it will answer very well. If you wish a perpendicular cylinder instead of a horizontal, I can construct it in that way, but it will not be so convenient for a portable engine. I have now engines with horizontal cylinders at work above ten years, and find them answer equally as well as a perpendicular cylinder.
"I remain, Sir,
"Your very humble servant,
"Richd. Trevithick.
"Jas. Green, Esq., Exeter."
Engineers nowaday are not in the habit of designing and constructing a steam-engine in six weeks, or willing to alter the agreed form from the horizontal to the vertical without charge.
[Rough draft.]