DE VRIES, Marion, American lawyer: b. near Woodbridge, San Joaquin County, Cal., 15 Aug. 1865. He was graduated from the San Joaquin Valley College in 1886 and from the law school of the University of Michigan in 1888. He practised law at Stockton, Cal., 1889-1900; was assistant district attorney of San Joaquin County in 1893-97, and was ad mitted to practice before the Supreme Court of the United States in 1897. From 1897-1900 he was a member of the United States House of Representatives. He became a member of the United States Board of General Appraisers, New York, 1900, and president from 1906-10. He resigned then, to accept the appointment of associate judge of the United States Court of Customs Appeals.
DEW, Thomas Roderick, American publi cist: b. King and Queen County, Va., 5 Dec. 1802; d. Paris, France, 6 Aug. 1846. He was graduated from William and Mary College, and in 1827 was elected professor of political economy, history and metaphysics; and in 1836 was made president of that institution. In 1829 he published his (Lectures on the Restric tive System.> It was brought out at a moment when feeling ran high on the subject of the tariff, between protectionists and free-traders; and though emanating from the closet of a thinker removed from the agitations of political warfare, took a strong hold on the public mind, and the subsequent adoption of the compromise of 1832 may be attributed in part to its silent influence. His 'Essay in Favor of Slavery' did much to decide Virginia's attitude. His most elaborate work was
DEW, a deposition of moisture after sun down upon the surface of the earth. Three concurrent sources of dew are recognized: (1) the condensation of the moisture of the atmos phere; (2) the condensation of watery vapor arising from the earth; and (3) the moisture exhaled by plants. Regarding the first of these sources, it is a well-known fact that warm air has a larger capacity for moisture than cooler air. Given a certain degree of humidity the falling of the temperature of the air after sun down will so reduce its absorptive capacity for the moisture that some of it will be condensed on objects colder than itself. Secondly, humid vapor rising warm from the warm soil comes in contact with the cooling strata of the at mosphere already depositing moisture and gives up its superabundance. In the third place, the grass, flowers and foliage which, under the action of plant life in sunlight have been evapo rating into the atmosphere the water absorbed by the roots to the sap so that it may be raised to the growing parts of the plant, continue this process until a balance is obtained between the temperatures at the roots and at the tips of the leaves. In some kinds of trees
this exhalation of moisture is very large and the dew thus formed may be heard dripping from the trees all night long. Most of the large, sparkling dewdrops seen on herbage in the early morning is this third form of dew. When the temperature of the lower air strata drops to 32° F., the dew is deposited as hoarfrost. When the sky is clouded the heat abstracted from the earth's surface by radiation is returned by the clouds, which, be ing good radiators, transmit an equal amount of heat to what they receive; and a balance of temperature being thus maintained between the earth and the surrounding atmosphere, no dew is formed. The deposition of dew is likewise prevented by wind, which carries away the air before the vapor has been condensed. Horizontal surfaces, and those which are ex posed to a wide expanse of sky, receive a greater supply of dew than sheltered or oblique sur faces, where circumstances diminish the amount of radiation.
An acquaintance with the cause which pro duces dew and hoarfrost enables us to under stand the rationale of the process resorted to by gardeners to protect tender plants from cold, which consists simply in spreading over them a thin mat or some flimsy substance. To ensure the full advantage of this kind of protection from the chill of the air, the coverings should not touch the bodies they are intended to defend.
The heavy dews which form in tropical regions are in the highest degree beneficial to vegetation, which, but for this supply of mois ture, would, in countries where scarcely any rain falls for months, be soon scorched and withered. But after the high temperature of the day the ground radiates under these clear skies with great rapidity, the surface is quickly cooled, and the watery vapor, which, from the great daily evaporation, exists in large quanti ties in the atmosphere, is deposited abundantly. This deposition is more plentiful also on plants, from their greater radiating power; while on hard, bare ground and stones, it is comparatively trifling. In cold climates the clouds, which are so common in damp and chilly regions, pre vent the radiation of heat: the surface is thus preserved warm, and the deposition of dew is, in a great measure, prevented. Consult Martin, E. A., Ponds) (London n.d.).