Philosophy of Manures. 343 



keep up a constant rarefaction and draught ; and the mouth of 

 all drains or pipes, for circulation of air, should be as wide- 

 expanded as possible. The chambers in which the pipes are 

 confined are improper, because the stratum of heated air con- 

 fined prevents both the conduction and radiation of heat. In a 

 brisk cold wind out of doors, Professor Leslie found the heat 

 carried off by conduction, owing to the constantly recurring 

 contact of cold air, nearly equal to that of radiation ; but in an 

 atmosphere of confined air, if perfectly confined, and of the 

 same heat as the iron itself, there will be no conduction at all. 

 Iron is a much better conductor than radiator of heat, and there 

 must be great loss in thus stopping nearly all the conduction of 

 heat. Professor Leslie's experiments also pointed out that the 

 effects of radiation on the differential thermometer diminished 

 in proportion as the air of the room was heated. As the radia- 

 tion of the thermometer itself would be less as the room was 

 heated, the difference would even be greater than that exhibited. 

 By surrounding the pipes with a stratum of confined air, we 

 thus diminish incalculably the effects of the pipes. Were the 

 pipes left free, or even in close contact with the masonry, with- 

 out a stratum of confined air intervening, the heat produced 

 would be greatly augmented. All iron pipes in houses should 

 be coated with lan)pblack. Professor Leslie found that, when 

 the radiating power of lampblack was estimated at 100, that of 

 polished iron was only 15; and though rough cast iron, and 

 rusted, will be much more, it will not have half the radiating 

 power of lampblack. The power of water to radiate heat is 

 equal to lampblack ; and, on this account, as also on account of 

 its simplicity, and the abundant source of moisture it supplies, I 

 think the open-gutter system of Corbett will excel all others, for 

 plant-structures at least. For fruiting-houses, the covers to the 

 gutters should be made to fit as closely to the water as possible, 

 when it is necessary to have dry air; as, if the water does not 

 touch the conveying-tube in all quarters, the confined air gene- 

 rated in the empty space inside will always cause a loss of heat, 

 in proportion to its surface. Of what use is it to carry the 

 heated water past the nonconducting stratum of air, to be again 

 deposited in the boilei'? As the heated smoke and air around 

 boilers, when allowed to escape from a chimney head, must 

 cause a great loss of heat, 1 think the plan of W. H., lately 

 stated in the Magazine, to combine a smoke-flue and pipes of 

 heated water in the same house, should be productive of a good 

 deal of economy. 



Kilmarnock, May 21. 1841. 



