Prevention of Frost.
—From the discussion of frost formation it is evident that, the temperature of the dew-point being the determining factor in its probable occurrence, any expedient that may be used either to increase the humidity or to conserve the radiation of heat would prevent a dangerous decline of temperature. Frost prevention is practised in all fruit-growing regions and the method pursued depends on the kind of vegetation to be protected.
In the protection of orchards the use of smudge pots are probably the commonest means for preventing the loss of heat. The object is to create a cloud of smoke over and about the orchard so that it forms a protective covering which prevents the escape of the heat.
In the case of a light frost—that is, where the temperature falls only a few degrees below the frost point—the plants in small gardens and flower beds may be prevented from freezing by liberal sprinkling with water. This is done to raise the humidity of the atmosphere surrounding the vegetation. Most vegetation withstands the temperature at the freezing point without particular injury, and the freezing of part of the water liberates heat in sufficient quantity to prevent a further decline of temperature. This heat liberated on the freezing of water is described in physics as the heat of fusion and in changing part of the water into ice sufficient heat is liberated to check the further fall of temperature.