Meteorology
that branch of science which observes, registers, classifies, METEOROLOGY METEOROLOGY and compares the various and varying while the thermometer falls and the phenomena of our atmosphere. It re- air becomes drier, N. W., N, or N. Ε. marks, at the same time, the connection wind, or less wind, may be expected; of those phenomena with heavenly bodies, and, on the contrary, if a fall takes place and with the solid and liquid materials with rising thermometer and increasing of the earth, in reference to their recip- dampness, wind and rain may be looked rocal and combined influence in deter- for from the S. E., S., or S. W.; a fall of mining the character of different climates, the barometer, with low thermometer, and with the view of learning the mete- foretells snow, with the barometer below oric history of every region of our globe, its ordinary height a rise foretells less of ultimately investigating the laws of atmospheric change and the plan of meteoric action; the theory, in fact, of meteorological phenomena, on which depends essentially the fitness of the various portions of the earth's surface of the production of different vegetable and other substances, and for the support of animal life.
It was not till the discovery of the barometer, in 1643, that the first great step was made toward a knowledge of the nature of our atmosphere. We were then, by its help, enabled to ascertain the weight and pressure of the great aërial ocean which surrounds us, and to learn when and where it was in a state of calm or storm. The invention of the thermometer, shortly afterward, gave the means of determining its temperature.
The hygrometer for showing the amount of moisture it contained, and the anemometer for giving the direction and force of the wind, are also instruments of great importance to the meteorologist.
The indications of these instruments, combined with the careful observation of atmospheric appearances, interpreted by the results of former observations, will enable the individual observer generally to predict the kind of weather that may be expected in his immediate locality for a day or sometimes longer in advance A strip of seaweed forms a very useful hygrometer for practical purposes, provided it be not kept in a room warmed artificially. In fine weather it will keep dry and have a somewhat dusty feeling, but with an increase of moisture in the air will become limp and sticky, indicating a probable change of weather in the shape of rain.
Since the discovery of the barometer, the science of weather forecasting has made much progress in its details, but, for the individual observer, the method remains much the same now as before.
The principal rule in use for forecasting the weather at present may be briefly stated as follows: A rising barometer usually foretells less wind or rain, and a falling barometer more wind or rain, or both; a high barometer fine weather, and a low one the contrary. If the barometer has been about its ordinary height at the sea-level, and is steady or rising, wind, or change in the direction toward the N., or less wet; but when the barometer has been low, the first rising usually precedes strong wind or heavy squalls from the N. W., N. or N. E., and continued rising foretells improving weather. If the barometer falls and warmth continues, the wind will probably back, and more S., or S. W. winds will follow.
At the present day, by the help of the telegraph, the meteorologist can obtain from as many stations as he desires the height of the barometer, direction and force of wind, etc., data which will inform him of the condition and movements of the aërial ocean at a definite time. He then marks on a map the height of the barometer at each place, and, drawing lines through all the places where the quicksilver stands at the same height, at any convenient interval he obtains a series of lines of equal pressure or weight, called shortly isobars, which show the height or depression at those places as the contour lines on a map show the different altitudes of the mountains and valleys. The thermometer readings, treated in the same way, are called isotherms. To make these synoptic charts (as they are called) complete, the force and direction of the wind, the amount of humidity, character of clouds, and other weather signs are also marked down, so that the chart may furnish a view of the weather at that particular time over the area from which reports have been obtained. Supposing now that at the same time the next day a new set of data are received and marked on another chart, a comparison of the two will show the nature and direction of the change going on, and enable the meteorologist to predict, to a certain extent, what will be the immediately coming weather. This is a general description of the way in which the forecasts of weather, printed in the daily papers, are made. ando
The World War brought about great activities in meteorological work, especially in relation to the atmosphere of aeronautics. Meteorological work was added to the routine activities of armies and navies with the duty of studying the atmosphere and the practical applica- Vol. VI-Cyc-N METER tion of the results to aeronautics. There was established in July, 1919, in Brussels, an International Union of Geodesy and Geophysics, one section of which is devoted to meteorology. New meteorological instruments include an improved pole star recorder, used for registering cloudiness of night. An improved snow sampler was also devised, as well as a new continuous recorder of atmospheric pollution. See WEATHER BUREAU.
METER. See METRIC SYSTEM.