318 



TUBULAR BOILER, SUPERHEATING STKAM, 



some engines perform double as much as others, under the same 

 known circumstances, and I believe that nothing but practice 

 will discover where this defect is, for, in my opinion, no state- 

 ment of theory yet given is satisfactory why high-pressure 

 engines so far exceed low-pressure engines. It is facts that 

 prove it to be so, therefore all theory yet laid down must be 

 defective." 



At the date of this letter Trevithick had been ratber 

 more than a year in England, residing generally at 

 Hayle, within half-a-dozen miles of Mount's Bay, from 



MOUNT'S BAY. [W. J. Welch.] 



whicb he bad sailed for America; and after eleven 

 years of wandering in countries where steam-engines 

 were unknown, except those that he himself had con- 



