CHAPTER II.
HEATING THE PLANT HOUSE.
The heating of plant-houses presents a difficulty proportioned to their size in an inverse geometrical ratio. To put the case in another way, it may be said, that the larger the house or group of houses to be heated the more easily may the desired end be accomplished, but the smaller the house the more difficult the task. In the preceding chapter it is remarked that the atmosphere of a small house is quickly influenced by changes of external temperature; and here it may be added that it is equally soon affected by the action of any kind of heating apparatus. Hence, the amateur who finds his plants hard frozen may light a fire to save their lives, and actually roast them to death in an hour or two, through indiscreet management. Nevertheless, the amateur who has but one small house need not be discouraged by this statement, for it is a part of the ostensible purpose of this book to render aid in this extreme but not uncommon case, as well as in the broader subject of heating in general.
It is of the utmost importance that the mode of heating should be thought of when a plant-house is designed in the first instance, because heat is generated and diffused, in accordance with fixed laws, to which all our arrangements must conform. Thus, if we build a house in a low, swampy position it will be found a difficult matter to give it the benefit of artificial heat by any means whatever, because as heat ascends from the level at which it is produced, it follows that the heat generator or furnace must be placed at a lower level than the house itself, and, in the case of a house in a swamp, the only place for the furnace will be in the water. This is another extreme case for which, so far as the laws of nature permit, we shall endeavour to provide; and it is cited simply for the purpose of impressing the amateur plant-grower with the neces-
