. Better fruit. Fruit-culture. Figure 2—"Key" Station A, Looking Nortliwest Clarkston, Washington vapor of water in the air, and it is just as invisible as the air itself. When the temperature falls to the dewpoint some of this vapor is condensed into water or ice spicules. The former may be dew and the latter frost. In the process of condensation the potential energy acquired during the process of vapori- zation becomes kinetic energy, and we say latent heat is liberated. It is assumed that the temperature of sat- uration, or, in other words, the dew- point will not change to any ma
. Better fruit. Fruit-culture. Figure 2—"Key" Station A, Looking Nortliwest Clarkston, Washington vapor of water in the air, and it is just as invisible as the air itself. When the temperature falls to the dewpoint some of this vapor is condensed into water or ice spicules. The former may be dew and the latter frost. In the process of condensation the potential energy acquired during the process of vapori- zation becomes kinetic energy, and we say latent heat is liberated. It is assumed that the temperature of sat- uration, or, in other words, the dew- point will not change to any material extent during the night, and if the dew- point is above freezing in the evening there will be sufTicient latent heat lib- erated when the thermometer reaches that point to prevent it from sinking any lower, and consequently there will be no frost the next morning. If, how- ever, the temperature of saturation is below freezing there is nothing to pre- vent the temperature from falling below that point and a frost is to be expected. If this theory fitted the facts it would be very easy to pre- dict frost, but unfortunately there are nights when the dewpoint is above thirty-two degrees that are followed by frost and nights when it is below that are not followed by frost. In the course of investigations by the writer he has come to the conclusion that in a very dry locality like that of the Yakima Valley a knowledge of the dewpoint the evening before is of very little value in determining whether or not to expect frost the next morning, but in the Rogue River Valley, and per- haps in the Boise district, it is helpful to the local man, but of no great benefit to the district forecaster. The informa- tion would be as helpful to the district man as to the local man if it were not for the lateness of the hour when the dewpoint observations must be taken to be of value. The local man can use the information if not available until nine o'clock at night, or even a little later, b
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