62 



POLMAISE METHOD OF HEATING HOTHOUSES. 



within the stove, from a collection of gases (and all economic 

 stoves, where of course the combustion is slow, are liable to such 

 occasionally), instead of the boiler or plates being blown out of 

 their place, these doors would be lifted outwards, and the evil 

 consequence avoided. Within the chamber, extending between 

 the two end walls of the stove, and bearing slightly on the end 

 wall of the hot-house, is a tank of water, F, divided longitudi- 

 nally, 4 inches deep, as shown in section, also by dotted lines in 

 ground plan, supplied by a check cistern from the outside, G, 

 also of course divided ; this may be furnished with a tap, by 

 which to empty it, or at which the gardener can always obtain 

 chilled water.* The roof of the hot-chamber is formed of 

 double slating, with a layer of M 'Neil's hair-felt and two or 

 three inches of sawdust between, and the upper surface is never 

 warm. From these arrangements it is evident that the entire 

 air of the hothouse, must flow over the plating, through the 

 chamber, and back over the tank of water (as shown by the 

 direction of the arrow in plan and section), and be returned back 

 into the hot-house in a heated form through the upper opening. 

 Here it is received into a large brick pit (as shown by inner lines 

 in plan), and it is allowed to escape through slate ventilators 

 from the sides and end of this pit. Iron bars extend across this 

 pit, and on these slates (thick duchess) are laid ; upon these 

 some pebbles and a few inches of tan as plunging material. To 

 those who have been accustomed to hot water, I may say, that 

 if they regard the cold-air main drain as the return pipe, the 

 chamber as an air-boiler, the brick pit as a hot-air tank, they 

 can be at no loss to understand either the arrangement or the 

 principle, and to perceive that there is no difficulty whatever in 

 reducing those principles to practice. And this brings me to 

 the third consideration I had proposed, namely, the advantages 

 likely to result from the employment of Polmaise heating ; and 

 the relative importance of these advantages will be differently 

 regarded by different classes of persons. The wealthy lover of 

 horticulture will first inquire, Can I grow my plants better? He 



* This cistern or tank is of very unnecessary extent : it is 5 feet long by 

 3 feet 6 inches wide ; if it were 18 inches or 2 feet, it would be ample to 

 supply the moisture necessary ; and this should be divided as in plan : for 

 a conservatory, a single trough 9 inches wide would be amply sufficient ; 

 and even this, as fires are only required in such structures in winter, when 

 much moisture is not required, would almost be unnecessary; it will be 

 observed from the position of the tank, that its under surface forms a sort 

 of roof to a flue, compelling the cold air to traverse the hot plate before 

 returning to the house : so that if the tank is dispensed with, some other 

 means must be taken to secure this — such, for instance, as a sheet of iron 

 plating or thin casting. My present tank will evaporate 50 gallons per 

 week ! 



