28 VARIOUS INVENTIONS. 



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 re- 

 volving bit was more suitable for drilling limestone 

 than the borer-chisel. The powdered stone was re- 

 moved from the hole by giving a screw form to the 

 stem of the bit. Many years afterwards precisely simi- 

 lar bits for boring wood were patented as new things, 

 and are still used. Within five months of his first com- 

 munication with the contractors for the Plymouth Break- 

 water 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 Eennie 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 



