Steam-Engines in Cornwall SB 



short of what had been obtained, whilst his superintendence 

 continued. 



The increasing depth of the mines requiring that the me- 

 chanical force should be augmented, a greater quantity of 

 steam became requisite. Mr Watt had already made the 

 boilers as large as he considered prudence to warrant, and ob- 

 tained an increased supply by using several boilers. But the 

 Cornish engine-builders imagined that the dimensions might be 

 enlarged, and that they might thus avoid the necessity of em- 

 ploying a greater number; the consequence of this mistake was, 

 that the boilers were made of the most unwieldy dimensions. 

 The theory of combustion was not in those days so generally and 

 accurately known as it is at present, and the fires in Mr Watt's 

 engines were of much larger dimensions than Mr Smeaton's ex- 

 periments, now confirmed by more extensive experience, have 

 demonstrated to be most consistent with economy of fuel. 



In some of the engines which were erected by the mine- 

 agents, the fire bars were placed more than ten feet below the 

 bottom of the boiler, as much as possible, and often nearly 

 the whole, of the intervening space, being filled with ignited 

 fuel. Under such circumstances, it must be evident that ten 

 millions would have been the extent of their performance. 

 From this general censure, we must, however, except several 

 engines erected by Mr Hornblower, particularly two large 

 double acting engines at the united mines, which, in propor- 

 tion and performance, were equal, if not superior, to any of 

 those which Messrs Boulton and Watt had erected in Corn- 

 wall, Mr Trevithick, who was a large contractor for the erec- 

 tion of steam-engines, made several ; but, as he paid but little 

 attention to the proportion of the parts, their performance was 

 not very good. His high pressure engine was first adopted, 

 in consequence of a scarcity of water for injection, and, among 

 many other excursions of his fruitful fancy, was the cylindri- 

 cal tube boiler, now generally used in Cornwall. About the 

 year 181 2, Mr Woolf came into Cornwall. He had also invent- 

 ed a boiler which was said to possess many advantages. It 

 consisted of a body or reservoir beneath, and connected with 

 which were several tubes, and between them the flame and 

 heated air traversed in their passage to the chimney. Being 



