78 POLE STEAM-ENGINE. 



stuffing box used to burn out, and a cloud of steam escaped. 

 The greatest difficulty was in the leaking of the boilers. You 

 could hardly go near them. Before that time we always put 

 rope-yarn between the lap of the boiler-plates to make the 

 seams tight. Captain Dick's high-pressure steam burnt it all 

 out. He said, ' Now you shall never make another boiler for 

 me with rope-yarn.' Everybody said it was impossible to make 

 a tight boiler without it. We put barrowfuls of horse-dung 

 and bran in Captain Dick's boilers to stop the leaks." l 



This difficulty of making a tight and safe boiler, that 

 puzzled Watt, was moonshine to Trevithick. When 

 the strained boiler and flinching rivets allowed the 

 boiler-house to become full of dense steam, Trevithick 

 told them to cover it up with ashes, they would not 

 see it quite so much then, and it would keep the heat in 

 the boiler. Bran or horse-dung inside was a good thing 

 as a stop-gap, though it added not to the strength of the 

 boiler. Trevithick was himself in a cloud of steam in 

 the engine-house ; yet, with such surroundings, he turned 

 on and off his gunpowder steam, from his cannon of a 

 pole-case, of 40 tons force, sending his bolt-shot pole, 

 33 inches in diameter, its destined course of ten feet, 

 and back again, as though it were a shuttlecock, several 

 times in a minute. 



Having by one or two years of experience proved the 

 value of his new pole-engine, he applied for a patent on 

 the 13th June, 18 15, 2 of which the following is the 

 portion referring particularly to the pole-engine : 



" Instead of a piston working in the main cylinder of the 

 steam-engine, I do use a plunger-pole similar to those employed 

 in pumps for lifting water, and I do make the said plunger-pole 

 nearly of the same diameter as the working cylinder, having 



1 Henry Clark of Redruth, in 1869, aged eighty-three years. 



2 See full copy of patent, chap. xvi. 



