Archive image from page 188 of Dairy farming being the. Dairy farming : being the theory, practice, and methods of dairying dairyfarmingbein00shel Year: 1880 PRACTICAL HINTS ON DRAINING. 1:27 continues to throw off lioat by radintion, and soon becomes cooler than the air, unless the same amount of heat be returned from other surfaces. Becoming cooler than the air, the soil or plants cool the air which comes in contact with them; and thus cooled to a certain point, the air cannot hold all the vapour which it absorbed while warmer, and part of it is deposited upon the soil, plant, or other co
Archive image from page 188 of Dairy farming being the. Dairy farming : being the theory, practice, and methods of dairying dairyfarmingbein00shel Year: 1880 PRACTICAL HINTS ON DRAINING. 1:27 continues to throw off lioat by radintion, and soon becomes cooler than the air, unless the same amount of heat be returned from other surfaces. Becoming cooler than the air, the soil or plants cool the air which comes in contact with them; and thus cooled to a certain point, the air cannot hold all the vapour which it absorbed while warmer, and part of it is deposited upon the soil, plant, or other cool surface. This is dew; and the temperature at which the air is saturated with vapour is called the dew-point. If saturated at a given temperature with vapour, the air, when cooled below this point, must part with a portion of the vapour in some way: in the form of rain or mist if in the air; in the form of dew if on the surface of the earth. ' If, however, other surfaces at night radiate as much heat back to the earth as it throws off, the surface of the earth is not thus cooled, and there is no dew. Clouds radiate heat to the earth, and, therefore, there is less dew in cloudy than in clear nights. If the temperature of the earth sinks below the freezing-point, the aqueous vapour is frozen, and is then called hoar- frost. Dew, then, is an effect, not a cause, of cold. It imparts warmth, because it can be deposited only on objects cooler than itself.' Some practical men think it necessary to give a direct admission of air to drains by con- necting the upf)er ends of minor drains with the surface of the land, and they do this by putting two or three of the ordinary pipes in a perpendicular or in a sloping position. It is true that no, or very little, harm is done by this method, but it is a sujerfluous thing to do; for if the soil was not easily penneable by air after draining, the draining itself could not possibly do any good, and if soils were air-tight they would also be wa
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