. My garden, its plan and culture together with a general description of its geology, botany, and natural history. Gardening. VENTILA TION OF GLASS-HOUSES. 77 is easy in theory but difficult in practice, as plants and all organic beings when at rest can very ill bear the air in motion. Whenever any portion of the air of a glass-house is cooled, it becomes heavy, and falls; whenever it is heated, it becomes light, and rises. In a cold night the pipes are at ioo° Fahr., the glass down to lO° : consequently the air whicli touches the pipes expands, becomes lighter, and rises rapidly ; the air whi
. My garden, its plan and culture together with a general description of its geology, botany, and natural history. Gardening. VENTILA TION OF GLASS-HOUSES. 77 is easy in theory but difficult in practice, as plants and all organic beings when at rest can very ill bear the air in motion. Whenever any portion of the air of a glass-house is cooled, it becomes heavy, and falls; whenever it is heated, it becomes light, and rises. In a cold night the pipes are at ioo° Fahr., the glass down to lO° : consequently the air whicli touches the pipes expands, becomes lighter, and rises rapidly ; the air which touches the glass cools, becomes denser, and falls to the bottom of the house. In any large greenhouse the descent of the chilled air in a cold night is apparent to the senses. From the weight of the cold air it is advisable that, as a general principle, a considerable part of the heat should be applied as low as possible. In a long house with excess of heat at one end the hot air rises and travels along the roof; whilst the cold air falls and returns by the floor to the source of heat, where it again ascends. In making arrangements for the heating of any specified house, the engineer should well consider all cooling surfaces, for he may be sure that the cold air from all such situations will fall to the floors as certainly as bullets would, if dropped from a similar position. In my Cucumber-house (fig. 92) and Melon pit, I let air into the house in contact with the hot metal and warm water. This in effect puts a pressure upon the air of the house, and the vitiated air escapes through every little crevice in the glass : this is a very safe system in cold weather. In all ventilating and heating arrange- ments, it is essential that the air should preserve its moisture, and my evaporators are useful to determine this point. When fig. 92.—Cucumber House, we warm the air it becomes too drying, and we must add water • and we do this at my garden by using open heated tanks of
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectgardening, bookyear18
