POLMAISE METHOD OF HEATING HOTHOUSES. 



57 



we do, and not that which we do not want, — so does Polmaise. 

 Common sense tells us that the air in a building which most 

 requires warming is the coldest, — Polmaise takes it first. Every- 

 body cries, " Pleat us uniformly ! " — Polmaise is the only mode 

 that can possibly approach to it. Having proved the truth of 

 the Polmaise principles of heating, I shall proceed to point out 

 the manner in which they may be easily reduced to practice. 



The coldest air in any building (whether room or hot-house) 

 is of necessity on the floor ; if it can pass below the floor it will 

 be there ; so that if a drain be made below the floor of a room, 

 with gratings opening into it, this drain will be instantly filled 

 with the coldest air of the room. Supposing this drain extends 

 into another building, and the air which it contains is at liberty 

 to pass over a heated surface, and having passed it can again flow 

 back at a higher level into the place from whence it came, it is 

 evident from the principles so recently laid down, that the whole 

 air of the room will flow over this heated surface and become 

 warmed, and that such currents of air will never cease till the 

 air of the two buildings is at nearly the same temperature ; and 

 consequently, that in proportion as we burn fuel, and heat the 

 surface employed, so must we by this means raise the temperature 

 of the air passing over it. 



Subjoined is a plan and section of the hot-house and stove, 

 showing the simple mode in which I propose to carry out the 

 Polmaise heating. 



The outer line of ground plan represents the walls of a hot- 

 house, the openings, C, are external ventilators for the purpose 

 of admitting fresh air ; these are exactly such as might be em- 

 ployed for any other system of heating ; they have no necessary 

 connection with Polmaise, and the heating principle acts, 

 whether they are closed or whether they are open. It is evident 

 that when open they admit fresh air into the house; and however 

 cold the weather, any air admitted by them, instead of cutting 

 the plants, as is the case when side-sashes are open, will immedi- 

 ately, from its great specific gravity, descend at once into the 

 cold-air drain, and become warmed before coming in contact 

 with the vegetation within the house. The number left open 

 will, of course, be dependent on external circumstances ; and 

 when they are all closed, the hot-house resembles any other hot- 

 house that is closed, and thus heating and ventilation are kept 

 apart, the requirements of the two necessarily being different. 

 Within the external walls is a walk round three sides of the 

 house, in which are openings, E, leading into drains, these 

 drains converging into a main drain, as shown by the arrows ; 

 these drains are formed of brick on edge-sides, and duchess 

 slates for roof, the soil forming their floor. The main drain is 



