TIIK \VAT r r AN'D THE TREVITHICK ENGINES. 187 



power of the steam-engine two or three fold without 

 additional consumption of coal. 



In the Wheal Towari engine the steam -cylinder 

 was 80 inches in diameter, with a 10-feet stroke. The 

 shaft was 900 feet in depth ; the main pumps 16 inches 

 in diameter; the pump-rods were of wood, about 

 14 inches square, and weighed more than the column 

 of water in the pipes. The boilers were Trevithick's 

 cylindrical with internal tube, wholly of wrought iron. 

 The cylinder and steam-pipes were surrounded with 

 sawdust about 20 inches in thickness, as a non-con- 

 ductor of heat. The upper surfaces of the boilers were 

 covered with a layer of ashes for the same purpose. 

 The duty performed was 86*58 millions of pounds of 

 water, raised one foot high by the consumption of a 

 bushel of coal weighing 84 Ibs. The immense power 

 and economy of this engine are best understood by its 

 average labour costing only One farthing in coal for 

 lifting 1000 tons one foot high. 



At or about that time an old intimate of Trevithick's, 

 Captain Nicholas Yivian, managed the mine, and Mr. 

 Neville, a shareholder, also a user of steam-engines in 

 Wales, observing the economical working of Wheal 

 Towan high-pressure steam expansive engine, doing 

 eighty-seven millions, requested its manager to examine 

 colliery engines, all of which were of the low-pressure 

 kind ; one of them was a Newcomen atmospheric, 

 whose duty was six millions ; four or five others were 

 Watt low-pressure steam vacuum engines, doing four- 

 teen millions ; therefore the high-pressure steam-engine 

 did six times as much work with a bucket of coal as the 

 low-pressure steam vacuum, and fourteen times as much 

 as the low-pressure steam atmospheric engine. Several 

 competitive trials by the county engineers were pub- 



