342 TUBULAR BOILER, SUPERHEATING STEAM, 



the weight of a Boulton and Watt engine will perform twenty 

 times the duty. 



" Air sides condensation will be advantageous on board ship, 

 because there are holes for the passage of water through the 

 bottom and sides of the s^ip. 



" I am anxious to have your opinion on this plan of returning 

 the hot anr from the condenser to the fire-place, and what you 

 think the effect will be. 



" The Comptroller of the Navy has not yet returned from 

 Plymouth, therefore no answer has been given to me. 



"You will see by the sketch how very small and compact an 

 engine is now. brought without complication or difficulty ; each 

 surface foot of boiler and condenser is equal to one-third of a 

 horse-power, weighing 20 Ibs., or 60 Ibs. weight for each horse- 

 power. The consumption of fuel is so small when working a 

 differential engine, that I expect it will not exceed 1 Ib. of coal 

 per hour for each horse-power. 



" The cost of erection and required room are so small from 

 its simplicity that it will be generally used. As I am very 

 anxious that every possible improvement should be considered 

 prior to making a specification for a patent, I must beg that 

 you will have the goodness to consider and calculate on the 

 data I have given you. I am sorry to trouble you, but I am 

 satisfied this will be to you rather a pleasing amusement than 

 a trouble. The warming machines will take a very extensive 

 run, and I believe will pay exceedingly well. 



" I am almost in the mind to take a ride down to see you in a 

 few days, but am now detained here about the American mining 

 concerns. 



" I remain, Sir, 



" Your very humble servant, 



"KD. TREVITHICK." 



The letters and foot-note are the only changes made 

 by the writer in Trevithick's original sketch so de- 

 scriptive of a wonderful application of varied and 

 improved principles of long-known difficulty and im- 

 portance; the beautifully compact tubular boiler for 



