12 VAK10US INVENTIONS. 



thus reduce the force of the air as to make it almost impossible 

 for that addition to add so much power as the blast takes 

 away. 



"I have, therefore, no hesitation in saying that this plan 

 will certainly not do. Write to me by all means whenever 

 anything strikes you, 'and you may always depend on having 

 my best advice. 



" I am, dear Sir, 



" Ever most truly yours, 



"DAVIES GIDDY." 



Trevithick saw without apparent reasoning, while 

 his friend's reasonings failed to make plain the full 

 bearing of the questions, and so cramped the position 

 as to make a change of front difficult an operation in 

 which Trevithick excelled. We learn, however, that 

 in 1801 he suggested a blast in copper-ore furnaces, 

 and in 1811 was on the verge of a discovery that has 

 since revolutionized the iron-smelter's art by the use of 

 hot blast. Wasted heat from a blast-furnace 10 feet 

 high led him to the conclusion that by doubling the 

 height of the furnace, enabling the cold mineral thrown 

 in at the top to take up the heat wasted through the 

 top of the low furnace, seven-eighths of the coal would 

 be saved. His idea of sending blast through the fur- 

 nace of his steam-boiler to economize heat could have 

 been readily applied to the iron furnace, and we should 

 have had the modern hot-blast iron furnaces. 



[Hough draft.] 



" GENTLEMEN, " CAMBORNE, March 5th, 1812. 



"Your favour of the 15th February, with a sketch of 

 your brewery, I have received ; and from which I find the head 

 of water is 30 feet above the brewery, which makes it difficult 

 to erect the chain and buckets so as to take advantage of the 



