METEOROLOGY, perewpov+Xemv erally the science of the things in the air. Meteorology has come to mean that part of natural philosophy that treats of the physics of the air and the mechanics of its motions. It includes climate (q.v.) and weather. The dis tinction in the meaning of the two terms is apparent when it is stated that one may well speak of the weather of to-day, or last month, or some past year, but not of the climate of a day, a month or a year, which is determined by finding the averages and the extremes of all the weather conditions for a long series of years: of the temperature, precipitation, hu midity, sunshine, cloudiness and wind velocity and direction.
Theoretical Meteorology aims to trace out the workings of definite laws to explain the various atmospheric phenomena, and properly may include a study of variations in solar ea& ation, as effecting the earth's temperatures, 07 as the primary causation of terrestrial storm Applied Meteorology strives to apply th theory of meteorology to the art of weaisr forecasting, which, so far, has not passed be yond the empirical stage, and in various wry to utilize knowledge of the physics of the r in the commercial industries.
History.— The term science was not apti. cable to man's knowledge of the atmosphere the time Virgil, Cicero and Aristotle wrote the weather. As late as the time of the found ing of the first of the 13 original colonies Jamestown, Va., in 1607, practically notbi..-, was known of the properties of the air or c: methods for the measuring of its phenomm. The development of the thermometer and TL: ricelli's invention of the barometer in lt-;.; made study and investigation possible_ American scientists may well be proud the services rendered by their countrymen humanity in adding to our knowledge of sip atmosphere. The act of the great Franklin drawing down the lightning of the clouds identifying it with the electricity of the lalsrn tory was but one of his important contribution to meteorological science. In 1747, while til ing observations at Philadelphia of a hr.:: eclipse, in co-operation with -his brother Boston, he learned that storms moving inn the west, as all storms of the middle latiiu do, first begin with easterly winds, and as approach a place of observation become wester". and he came near discovering the cyclonic tern of storms. Following the winter of lfS.1 famous in history for the phenomenal severi: of its cold, and its long duration, Franklin. a letter to a correspondent in Europe, milt: attention to the violent eruption of Hecla the preceding year, and suggested Ina: the dust therefrom may have been carried ir-u the high strata of the atmosphere and sprea:. around the earth by the winds. His idea wk. that this dust would screen off some of sun's rays and add to the cold of winter. in many other things, he had a prophetic visiew_ for there no longer is doubt that violent vol canic eruptions throw into the upper air large quantities of dust particles which, by swath moving easterly currents in the middle latina..
and westerly currents in the tropics, are so... so distributed around the earth as not onl.i effect the colors of the sky for two or that years after, but to modify the weather. less the earth in this year of 1919 still is fm:. ing the cooling effects of the explosion • Katmai, in the Alaskan Peninsula, in 1;1:. augmented by volcanic explosions in Japan 1913.
The author of the Declaration of Indepv-! ence, Thomas Jefferson, took daily observation of the weather. He even carried his tN1 mometer to Philadelphia and twice recorde; the temperature of Independence Hall or July 1776. He owned one of the only nu barometers then in the colonies. In co-opens tion with James Madison (after bishop). •i) lived at Williamsburg,•some 200 miles east Monticello, he determined that changes in ire barometer first begin several hours earlier .1 the westernmost station. The British ransackx= his home and broke his barometer. It is -at' that he berated them more for the destruction of his cherished instrument of the weather than he did for their burning of the National Capi tol. As early as 1735 Hadley, an Englishman, had published an article explanatory of the trade winds, and Dalton, another Englishman, in 1793, made the first attempt to explain the phenomena of the atmosphere through the prin ciples of philosophy. It was then believed that storms were straight-line gales. It remained for Redfield, an American, in 1831 to publish an epoch-making essay, in which storms were described as progressive whirlwinds, turning counter clockwise, with an easterly movement of translation for the whole system of spirally in-flowing air. Espy followed, in 1841, and showed that rainfall is caused by ascending cur rents, cooling by expansion as they rise until the water vapor becomes saturated. By the same line of reasoning he explained how de scending air must heat by compression. In 1843 Tracy made an important contribution to the subject. Redfield had claimed that the air in storm-whirls neither moves in concentric curves nor along radical lines into the interior of the storm, but spirally inward. Tracy proved that Redfield was right, for he showed that the rotation of the earth must deflect all air cur rents to the right of the initial direction in the northern hemisphere, whether in storm-whirls or out of them. From 1840 to 1860 the other Americans who added most to our knowledge of meteorology were Maury, Coffin, Henry, Lapham and Loomis. Mathew Fontaine Maury, of the United States navy, was the pioneer in marine meteorology. He mapped the oceans and determined the direction and force of winds and water currents. In 1855 he published his Physical Geography of the Sea and its Meteor ology.' See WEATHER BUREAU.