POLMAISE MODE OF HEATING GREEN-HOUSES- 



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An equal and uniform temperature in all 

 parts of the house ; a constant circulation 

 being maintained of heated air towards the 

 coldest part of the house, and cold air to 

 the warmest part. 



Improved health of the plants, caused by 

 the fresh warm air (rendered moist by 

 passing- over a small tank or pan,) circu- 

 lating freely in all parts of the house. 



A much smaller consumption of fuel to 

 produce a given temperature than in any 

 other mode of heating. 



Economy in construction ; the cost being 

 not more than a third that of hot water 

 pipes, and somewhat less than that of flues. 



This method of heating has now been 

 practiced for three years in various parts of 

 Great Britain ; and though, like all inno- 

 vations, it has met with opponents among 

 those whose interests or prejudices bias 

 them in favor of the old modes, it appears 

 now to be pretty generally conceded that 

 "Polmaise," as it is familiarly called, is a 

 great step in advance of the previous modes 

 of heating horticultural buildings. 



Several of our correspondents, anxious to 

 make a trial of it in this country, have so- 

 licited from us details of its construction 

 and operation. We therefore endeavor to 

 place the matter as clearly and concisely 

 as possible before them. 



The principle of the Polmaise method is 

 one long well known in science, viz., that 

 cold air descends, and hot air ascends; 

 and that a vacuum being caused by ab- 

 stracting a portion of the air from one part 

 of a room, it will be directly filled by a 

 corresponding quantity of air that will flow 

 in to supply its place from another part of 

 the room. 



In a hot-house, heated in the ordinary 

 manner, by flues or hot water pipes, run- 

 ning round at the level of the floor, the 

 warmest part of the house is at the apex of 



the roof, and the coldest part at the floor ; 

 because the heated air rises, and the cold 

 air settles at the bottom, and there is little 

 or no circulation. From this want of cir- 

 culation, there is also an accumulation of 

 heat about that part of the house nearest 

 the boiler or furnace ; and, in very severe 

 weather, the plants there are liable to be 

 injured by heat, while those in the opposite 

 end are with difficulty kept from the ill 

 effects of cold. A considerable part of the 

 heat produced by the furnace or boiler is 

 also lost in the mass of materials that sur- 

 rounds it. 



In a hot-house or green-house, heated by 

 Polmaise, the constant motion of the air 

 from the furnace towards the coldest end of 

 the house, and from the latter back again to 

 the furnace, distributes the heat uniformly 

 throughout the whole of its area. While, 

 as we shall see, by small openings provided 

 in the wall near the level of the floor, fresh 

 air is admitted, passes at once into the cold 

 air drain, over the furnace and into the 

 house, — thus providing a complete system 

 of ventilation, without any of the injurious 

 effects of cold drafts through open doors or 

 windows in the common mode. 



To illustrate our meaning, we submit the 

 two following cuts, showing the section and 

 ground-plan of an ordinary lean-to green- 

 house, heated by Polmaise. In Fig. 20, 

 A is the green-house, B the back shed, — 

 the latter containing the sunk area or stoke- 

 hole ; C, for feeding the furnace ; d, is the 

 level of the floor. 



In this section, 1 is the furnace, with an 

 air chamber, 2, all round it ; 3 is the cold 

 air drain ; 4 the register, or opening in the 

 hot-air chamber, through which the heated 

 air passes into the house. 



In Fig. 21, 2 is the furnace and hot-air 

 chamber with its opening, 4, for the exit of 

 the hot air; 3 the cold-air drain. This 



