THE WATT AND THE TREVITHICK ENGINES 135 



not satisfy them, neither will I unless they pay me for it in 

 some way or other. If you direct for me at the Dale it will 

 find me. I am happy to find that you have a seat in the House. 

 I wish every seat was filled with such. 



" I remain, Sir, 



" Your very humble servant, 



u KlCHARD TllEVITHICK." 



Trevithick fully understood the value of the expan- 

 sive principle in 1804 : when working with steam of 

 45 Ibs. to the inch, the engine went at a speed of 

 twelve strokes a minute. On cutting off the steam at 

 half-stroke, the speed and consequent work done fell 

 to ten and a half strokes a minute ; in other words, the 

 work performed by the engine fell off only one-eighth 

 part, while the quantity of steam and consequently of 

 coal was reduced by one-half. The principle was esta- 

 blished, but the application was practically incomplete 

 from the want of heavier fly-wheels, to give out their 

 momentum during the latter half of the stroke, when 

 the expanding steam was lessening its force. 



" The saving of coal would be very great by working 

 expansively, but as coal is not an object here," Mr. 

 Homfray was careless about the expansion. Thirty- 

 three years after this indirect check to steam-engine 

 economy, the writer, then living in the Sirhowey Iron 

 Works, and within stone's - throw of Mr. Homfray's 

 Works, recommended the removal of the Boulton and 

 Watt's waggon boilers, to make room for Trevithick's 

 boilers, on the plea of saving one-half the fuel, and at 

 the same time increasing the power of the engine, and 

 thereby the pressure of the blast in the iron furnaces. 

 The proprietor was careless about the saving of coal, 

 and was doubtful that an increased blast would increase 



