148 THE WATT AND THE TREVITHICK ENGINES. 



and another new engine of mine to be built immediately. The 

 great boiler for the old engine is not yet ordered. 



" I have received orders for nine engines within these four 

 weeks, all for Cornwall. Two 12-inch cylinders, two 16-inch 

 ditto, three 9-inch ditto, one 8-inch ditto, one 7-inch ditto. I 

 expect one will be put to work next week at Wheal Abraham, 

 for lifting water. 



" This day I shall leave Cornwall for London. Shall stop 

 two days in the neighbourhood of Tavistock, and take orders for 

 three engines. As soon as I arrive in town I will call at your 

 lodgings. I expect that the patent will be brought into court 

 about the end of May. A person in Wales owes us about 600?. 

 patent premium, and he says that the patent is not good. More 

 particulars you shall have on my arrival. 



" The railroad is going forward. I have the drawings in hand 

 for the inclined plane. 



" I am, Sir, 



" Your very humble servant, 



" ED. TREVITHICK." 



The fact that expansion of steam caused reduction 

 of heat was so evident to Trevithick that he ventured 

 to doubt his friend's theory. The trials between the 

 whim-engines having continued a fortnight, showed 

 that -the high-pressure steam-puffer had lifted 83 cwt., 

 while the low-pressure steam vacuum only lifted 26 cwt. 

 with the consumption of a bushel of coal. A suitable 

 high-pressure boiler for the Watt low-pressure steam 

 63-inch pumping engine should be 30 feet long, 8 feet 

 in diameter, with an internal fire-tube 5 feet in dia- 

 meter; proportions approved of in the present day. 

 The recommendation in 1806 to use small tubes may 

 claim to be the first practical decision on the advantage 

 of tubular boilers ; and at the same time we read of 

 the first hesitating step on the part of the public to use 

 high-pressure steam in a Watt low-pressure engine, 



