360 TUBULAll BOILER, SUPERHEATING STEAM, 



forms the hot well. The tubes are horizontal over the fire, the 

 water circulating through them. The condensed steam is 

 pumped into the well at a temperature of 100, and being there 

 subjected to the heat radiating from the furnace, is pumped 

 back into the boilers at nearly boiling point. It is estimated 

 that, under these conditions, the pinnace would run for nearly 

 48 hours without having to ' blow off ' or carry a supply of 

 fresh water, the waste water being made good by sea water." * 



The peculiarity of this steam-pinnace of 1871, on 

 which a patent was granted, is stated to be a metal 

 surface condenser exposed to the cold water at the 

 bottom of the boat, returning the condensed steam at 

 about boiling temperature to the boiler, and a vertical 

 boiler with horizontal tubes through which the water 

 circulates, both of which in principle, if not in detail, 

 are seen in the surface condenser of Trevithick's iron- 

 bottom ship of 1809, and his vertical boiler of 1816, 2 

 and further illustrated in the inventions spoken of in 

 this and the following chapter ; and yet on so all- 

 important a subject, dealt with in various ways by 

 Trevithick from 1804 to 1832, his plans are reproduced 

 as discoveries in 1871. 



About 1828, Mr. Rennie, Mr. Hen wood, and others, 

 reported on the advantages of high-pressure expansive 

 steam in "Wheal Towan engine, 3 on the north cliffs of 

 Cornwall, near Wheal Seal-hole Mine on St. Agnes 

 Head, where in 1797 Trevithick had worked his first 

 high-pressure steam-puffer engine in competition with 

 the Watt low-pressure steam-vacuum engine. Captain 

 Andrew Yivian was then his companion, and the Cow 

 and Calf, two rocks of unequal size, a mile from the 

 land, were from that time called Captain Dick and 



1 < The Times,' November 24th, 1871. 



2 See vol. i., pp. 336, 364, 370. 



See Mr. Kenwood's report, vol. ii., p. 185. 



