. The principles of fruit-growing, with applications to practice. Fruit-culture. Predicting Frost 253 sideration, because they may be obtained early in the day, before it is possible to secure any reliable indica- tions from local observations as to the probability of frost. But when the warnings issued by the Weather Bureau cannot be obtained, and the farmer must rely on • himself, there are no instrumental readings that will take the place of a careful observation of the condi- tion of the sky, the direction and force of the wind, and the trend of the ; "In the day, pla
. The principles of fruit-growing, with applications to practice. Fruit-culture. Predicting Frost 253 sideration, because they may be obtained early in the day, before it is possible to secure any reliable indica- tions from local observations as to the probability of frost. But when the warnings issued by the Weather Bureau cannot be obtained, and the farmer must rely on • himself, there are no instrumental readings that will take the place of a careful observation of the condi- tion of the sky, the direction and force of the wind, and the trend of the ; "In the day, plants usually receive more heat from the sun than they give off (radiate), and conse- quently become warmer; but at night the process is reversed, and they radiate .more heat than they receive and thus grow colder. When the surface of a plant has lost (radiated) sufficient heat to cause its temperature to fall to 32° or below, frost forms. Any condition that causes increased radiation will increase the liability of frost, and conversely, whatever checks radia- tion or supplies additional heat to the air will tend to ward off ; Favorable con- ditions for frost are a clear night, a quiet or still night, a moderately dry atmosphere. The surface air is likely to be colder than that above, so that a wind may warm the surface air by mixing it with the warmer strata. Wilson makes the following observations on weather conditions as indicating frost:. Fig. 93. One form of a wet-and-dry bulb hy- Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bailey, L. H. (Liberty Hyde), 1858-1954. New York : Macmillan
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