AND SURFACE CONDENSER. 325 



\\;itor in the condenser cistern was at 50. After working for 

 twenty-five minutes the small quantity of hot water discharged 

 at the top of the air-pump reached 130 of heat, but then would 

 rise no higher, the cold sides of the condenser being equal to 

 the condensation of all the steam. The eduction-pipe and air- 

 pump, with its bottom and top, gave 60 feet of surface sides of 

 thick cast iron, and about 20 feet more of surface sides of a thin 

 copper condenser; altogether, 80 feet of surface cold sides, 

 surrounded by cold water. About half a pound on the inch was 

 lost in the vacuum, the discharged water being 130 of heat 

 instead of 100. The vacuum was made imperfect by about 

 1^ Ib. to the inch. 



"It is my opinion that high steam will expand and contract 

 with a much less degree of heat or cold in proportion to its 

 effect, than what steam of atmosphere strong will do. I intend 

 to try steam of five or six atmospheres strong, and partially 

 condense it down to nearly one atmosphere strong, and then by 

 an air-pump of more content than is usual to return the steam, 

 air, and water, from the top of the air-pump, all back into the 

 boiler again, above the water-level in the boiler, and by a great 

 number of small tubes, with greatly heated surface sides, to re- 

 heat the returned steam ; though by this plan I shall lose the 

 power of the vacuum, and also the power required on the air- 

 bucket to force the steam and water back again into the boiler, 

 yet by returning so much heat I shall over-balance the loss of 

 power, besides having a continued supply of water, which in 

 portable engines, either on the road or on the sea, will be of 

 great value. 



" I shall esteem it a very great favour if you will be so good 

 as to turn over in your mind the probable theory of those 

 statements, and give me your opinion. If Mr. Watt's reports 

 of his experiments are correct, how is it possible that the high- 

 pressure engine that I built at the Herland thirteen years ago, 

 which discharged the steam in open air, did more than twenty- 

 eight millions ? If you wish, I will send a copy of the certifi- 

 cate of the duty done by this engine, which states very minutely 

 every circumstance. Now that cylinder, with every part of the 

 engine, was exposed to the cold ; had it been heated around 



VOL. n. '/. 



