276 



THE TROPICAL HOUSE. 



ventilating a hot-house the operation ought to begin by letting down the 

 top lights, or opening the top ventilators (if such exist), to an extent vary- 

 ing according to the state of the weather, for opening either to the extent 

 of two inches when the external air is at the freezing point will be equal 

 to opening the same to the extent of four inches when the external air is 

 about forty-five or fifty degrees of temperature, or to a foot or more when 

 the thermometer indicates summer heat in the open air, because then 

 the external and internal air is nearly upon a par, and the circulation is 

 nearly stationary, whereas in the former cases the circulation is extremely 

 rapid ; the cold air without, by its gravit)^, forcing its way into every 

 little opening over the whole surface of the house, and forcing the 

 warmer and lighter air out of the top openings ; in this way the whole 

 volume of air mthin a stove is changed in a very short time. It is 

 necessary for summer operations to have some of the front or lower lights 

 in the stove moveable, or to have (what we think a better plan) venti- 

 lators in the fi'ont or parapet wall. By a judicious working of these in 

 conjunction with the top hghts, ventilation will be most effectually at- 

 tained. There are few things in gardening less understood than the 

 theory of ventilation, although it is daily in use in every kind of structure, 

 from the hand-glass to the most magnificent conservatory ; the operator 

 too often opening that part of the structure most convenient to himself, 

 ■v\4thout once thinking of the consequences. We beheve that the first 

 correct principles upon this subject were laid down about thirty years 

 ago, by W. Atkinson, Esq., and first exemphfied in the hot-house of tlie 

 Earl of Mansfield, at Scoone Palace, in Perthshire, under his superin- 

 tendence. We remember w^ell the opposition his theory met with 

 amongst practical men long before we had the pleasure of that excel- 

 lent person's acquaintance, to whom we owe far more information on 

 the subject of hot-house architecture than to all the books we have 

 perused. 



Some very curious mechanical propositions have been advanced by Mr. 

 Kewley and others, on the possibihty of constructing self-acting venti- 

 lators ; but these have not as yet arrived at that degree of perfection to 

 warrant our recommending them. 



HEATING. 



Next to ventilation, as respects houses for the cultivation of tropical 

 plants, is the subject of a judicious and economical method of heating 

 them ; but this subject we have treated on so fully in the early part of 



