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POLMAISE METHOD OF HEATING HOTHOUSES. 



four feet wide and one foot deep, so that by laying a brick flat 

 and four courses high in the centre, and bricks on edge at the 

 sides, two common duchess slates reach to form the roof, and on 

 these is spread some sifted soil to make the drain air-tight ; the 

 centre brickwork forms a support on which in several places to 

 build up single brick piers to support the iron rafters which 

 carry the slates, on which rests the plunging-bed, as shown in 

 longitudinal section. This main drain, which should be slightly 

 on the descent towards the chamber, pierces the end wall of the 

 hot-house, the foundation being left out at that point, the end 

 wall of the house being there carried by York flagging, with a 

 centre support ; and thus the means are provided for allowing 

 the cold air to travel from the house to the chamber. The 

 openings at E, in the hot-house at Nutfield, are regulated by 

 sliding lids, made of slate, for the purpose of experiment ; this, 

 for practical purposes, is unnecessary, and in many cases it will 

 be found very convenient to make the cold-air openings in the 

 centre of the house concealed by some ornamental stage, the 

 floor of the walk forming the roof of the cold-air main drain ; or 

 handsome ventilators might be inserted at once in the roof of the 

 main drain, to take down the cold air. These points of detail 

 architects will arrange to suit different places, the great and 

 essential point being to provide a means for the cold air at the 

 extreme end of the house to pass to the hot chamber. The 

 outer wall of the hot chamber is built of 4^ -inch brickwork ; 

 this chamber is air-tight, as far as regards the external air, 

 having two openings on the side next the house on different 

 levels, the lower one to admit the cold air, the upper one to allow 

 its return when heated. The stove occupies the chief portion of 

 the chamber, standing isolated within it, except at the points 

 where the fuel is supplied and the ashes removed, and where the 

 return-flue passes into the chimney. The area left between the 

 wall of the stove and the wall of the chamber is two inches, 

 except on the side next the hot-house, where of course there is a 

 larger area to allow the cold air to rise and flow over the plate ; 

 but it will probably be found desirable to sink the top of the 

 stove to a level with the cold-air drain. The stove is formed of 

 four walls of 9-inch brickwork ; the outside measure is 5 feet 

 5 inches long, 4 feet 4 inches wide ; the internal measure, 

 therefore, 3 feet 10 inches long, and 2 feet 10 inches wide. 

 Another wall of the same substance is carried up between the 

 two ends, but not in the centre ; it is 16 inches from the wall of 

 the stove next the hot-house, and of course leaves a space of 

 9 inches between itself and the farther wall. It will be seen by 

 plan, that this wall and the one next the hot-house form the 

 actual furnace or fuel box ; in part of their length, where such 



