Connecticut western news., 1882-10-18
FROST INDICATIONS.
HOW FARMERS MAY BE FoREWARNED AGAINST LOW TEMPERATUREs-Av VAIL LIABLE CONTRIBUTION FROM THE UNI. TED STATES SIGNAL SERVICE,

LIABLE CONTRIBUTION FROM THE UNI, | TED STATES SIGNAL SERVICE.
 The latest paper emanating from the United States Signal Office is one that calls for the strict attention of farmers and all others dealing in goods affected ny changes in temperature. '"To fore- tell frost IS the title." ''At all temper atures," says the writer, Lieutenant James Allen, ''even the lowest, moisture exists in the atmosphere in an invisible state; the air Is never absolutely dry. The intervals between the particles of air are partly filled with the vapor that Is constantly rising from the earth. This capacity of the air for moisture has limit, and when this is reached the air Is said to be saturated. A rise of tenn perature increases the capacity of the air for moisture. On the other hand a fall of temperature diminishes the capacity. But the capacity of the air for moisture increases more rapidly than the temperature. Thus, air can contain at 32 degrees the 160th part of it's own weight, at 59 degrees the 8Oth part and at 86 degrees the 10th part, the law be- ing that for every increase of 27 degrees the capacity is doubled" After show ing how the amount of vapor in the air may be measured by noting the temper ature at which the moisture begins to be condensed on a cold vessel the writer gives full description of the dry and wet bulb hygrometer, and illustrates the manner in which the "dew point" can be ascertained by it's use. Regard | ing its usefulness to agriculturists he says: ''The ascertainment of the dew point is of great practical importance, particularly to horticulturists, since it shows the point near which the descent of the temperature of the air during the night will be arrested. For when the air has been cooled down by radiation to this point dew Is deposited and latent heat is given out. The amount of heat thus set free being great the tempera- ture of the surrounding air Is imme- diately raised. The same process con- tinues to be repeated, and thus the tenn perature of the air ill contact with plants or other radiating surfaces may be con- sidered as gently oscillating about the dew point. For if 1t raises higher the loss of heat by radiation speedily low CTS it. Thus the dew point determines the minimum temperature of the sur- face of leaves on the ground during the night. The minimum temperature in the instrument-shelterw would be higher than this.
 "This suggests an important practical use of the hygrometer. If the dew point be ascertained by it the approach of low temperatures or of frost may be foreseen and provided against. Thus, suppose on 8 fine, clear day, toward evening, that the dry bulb is 50 degrees and the wet bulb 40 degrees, the dew point at the time is, therefore, 20 de- grees Fahrenheit. Frost on the ground may then be predicted with certainty, and no time ought to be lost in protect ing such tender plants as may be ex- posed ln the open air. If, on the other hand, with sky quite as clear, the dry bulb is 50 degrees and the wet bulb AZ degrees, the dew point being thus 43 degrees, no frost need be feared. As stunning the sky to remain perfectly clear of haze or clouds, the raising or depressing of the dew point during the night Casually with change of wind) are the only circumstances that can happen to interfere with the predictions founded on the hygrometer. Frequently the presence of haze at high attitudes during the night prevents the radiation of heat from the earth and thereby the frost which otherwise would have oc- cured. Hoar frost is formed under the same circumstances as dew, with the exception of lower temperature. When the temperature of the surface of plants falls below 32 degrees the moisture of the air is condensed upon them in the solid state and forms layer of snow crystals like spongy ice. Roar frost, therefore, is not frosen dew but the moisture of the air is deposited in the solid form, without having passed through the liquid condition. Hoar frost, like dew, is deposited chiefly upon those bodies which radiate best, such as plants and the leaves of vegetables, and the deposit is made principally on those parts which are turned toward the sky. Since plants sometimes become cooled by radiation from 12 to 15 degrees be. low the temperature of the surrounding air, frost may occur although ther- mometer few feet above the ground, in an instrument-shelter, may not sink to 32 degrees. During clear and still night, when @ thermometer six feet above the ground sinks to 36 degrees, a heavy frost may be expected; slight rost may occur when the same ther- mometer sinks only to AZ degrees. Whatever prevents the radiation of heat serves also to check the formation of hoar frost. During the cold nights of spring, plants which are sheltered by trees are less liable to be injured by frost than those which are fully exposed, and thin covering of cloth or straw will generally afford entire protection. A garden may frequently be saved from injury by kindling small smudge fire. which will envelop the plants in cloud of smoke. Fogs and clouds also pro- tect vegetation from the effects of frost"
 All persons desiring to use the hy- grometer will be supplied with them by the Chief Officer of the Signal Service at cost price, seven dollars. Full in- structions as to the manner of reading