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METEOROLOGY (Gr. JerEwpa, and hb'yos,...

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Originally appearing in Volume V18, Page 271 of the 1911 Encyclopedia Britannica.
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METEOROLOGY (Gr. JerEwpa, and hb'yos, i.e. the science of things in the air), the modern study of all the phenomena of the atmosphere of gases, vapours and dust that surrounds the earth and extends to that unknown outer surface which marks the beginning of the so-called interstellar space. These phenomena may be studied either individually or collectively. The collective study has to do with statistics and general average conditions, sometimes called normal values, and is generally known as Climatology (see CLIMATE, where the whole subject of regional climatology is dealt with). The study of the individual items may be either descriptive, explanatory, physical or theoretical. Physical meteorology is again sub-divided according as we consider either the changes that depend upon the motions of masses of air or those that depend upon the motions of the gaseous molecules; the former belong to hydrodynamics, and the latter are mostly comprised under thermodynamics, optics and electricity. History.—The historical development of meteorology from the most ancient times is well presented by the quotations from classic authors compiled by Julius Ludwig Ideler (Meteorologia veterum graecorum et romanorum, Berlin, 1832). We owe to the Arabian philosophers some slight advance on the know-ledge of the Greeks and Romans; especially as to the optical phenomena of the atmosphere. The Meteorologia of Aristotle (see Zeller, Phil. der Griechen) accords entirely with the Philosophica of Thomas Aquinas, the poetic songs of the troubadours, and the writings of Dante (see Kuhn's Treatment of Nature in Dante's Divina Commedia; London, 1897). Dante's work completed the passage from the ancient mythological treatment of nature to the more rational recognition of one creator and lawgiver that pervades modern science. The progress of meteorology has been coincident with the progress of physics and chemistry in general, as is shown by considering the works of Alhazen (1050) on twilight, Vitellio (1250) on the rainbow, Galileo (16o7) on the thermometer and on the laws of inertia, on attractions and on the weight of the air, Toricelli (1642) on the barometer, Boyle (1659) on the elastic pressure of the air in all directions, Newton (1673) on optics; Cavendish (176o), elastic pressure of aqueous vapour; Black (1752), separation of carbonic acid gas from ordinary air; Rutherford (1772). separation of nitrogen; Priestley and Scheele (1775) and Cavendish (1777), separation of oxygen; Lavoisier (1783), general establishment of the character of the atmosphere as a simple mixture of gases and vapour; De Saussure's measurement of relative humidity by the accurate hair hygrometer (178o), Dalton's measurement of vapour tension at various temperatures (1800), Regnault's and Magnus's revision of Dalton's tension of water vapour (184o), Marvin's and Juhlins's measurements of tension of ice vapour (1891), and the isolation of argon by Rayleigh and Ramsay (1894). Theoretical meteorology has been, and always must be, wholly dependent on our knowledge of thermodynamics and on mathematical methods of dealing with the forces that produce the motions within the atmosphere. Progress has been due too. the most eminent mathematicians at the following approximate dates: Sir Isaac Newton (167o), Leonhard-Euler (1736), Pierre Simon Laplace (178o), Jean Baptiste Joseph Fourier (1785), Simon Denis Poisson (1815), Sir George Gabriel Stokes (1851), Hermann von Helmholtz (18.57), Lord Kelvin (186o), C. A. Bjerknes (1868), V. Bjerknes (1906), and to their many distinguished followers. The earliest systematic daily record of local weather phenomena that has survived is that kept by William Merle, Cohen, Meteoritenkunde (Stuttgart, 1894-1905) ; L. Fletcher, An rector of Driby, during seven years 1331-1338: the manuscript Introduction to the Study of Meteorites, loth ed. (London, 1908); I is preserved in the Digby MS., Merton College, Oxford, and was published in facsimile by George G. Symons in 1891. Doubt-less many similar monastic diaries have been lost to us. In 1653 Ferdinand I_I. of Tuscany organized a local system of stations and daily records which extended over and beyond northern Italy. This was the first fairly complete meteorological system in Europe. The records kept during the years 1655—1670 at the Cloister Angelus near Florence were reduced by Libri, professor of mathematics at Pisa, and published in 183o. The history of meteorology is marked by the production of comprehensive treatises embodying the current state of our knowledge. Such were Louis Cotte's Traite de meteorologic (Paris, 1974) and his Memoires sur la meteorologie, supplement au traite (1788); Ludwig Karatz's Lehrbuch der Meteorologie (Halle, 1831—1836) and his Vorlesungen (184o; French 1842, English 1845); Sir John Herschel's Meteorology (London, 1840); the splendid series of memoirs by H. W. Brandes in Gehler's Physikalisches Worterbuch (Leipzig, 1820—1840); E. E. F. W. Schmid's Grundriss 'der Meteorologie (Leipzig, 1862); Ferrel's Recent Advances in Meteorology (Washington, 1885); the great works of Julius Hann, as summarized in his Handbuch der Klimatologie (1883; 2nd ed., Stuttgart, 1897; vol. i.. English 1903) and his Lehrbuch der Meteorologie (Leipzig, 1901,,2nd ed. 1906); the extensive studies of J. E. Woeikoff (Voeikof), as presented in his Klima der Erde (Russian 1883, German 1885) and his Meteorologte (Russian 1904). The development of this science has been greatly stimulated by the regular publication of special periodicals such as the Zeitschrifl of the Austrian Meteorological Society, 1866—1885, vol. 21 appearing with vol. 3 of the Meteorologische Zeitschrifl of the German Meteorological Society in 1886, and since that date this journal has been jointly maintained by the two societies. The analogous journals of the Royal Meteorological Society, London, 1850 to date, the Scottish Meteorological Society, 186o to date, the Meteorological Society of France, 1838 to date, the Italian Meteorological Society, and the American Meteorological Journal, 1885—1895, have all played important parts in the history of meteorology. On the other hand, the Annals of the Central Meteorological Office at Paris, the Archie of the Deutsche Seewarte at Hamburg, the Annals and the Repertorium of the Central Physical Observatory at St Peters-burg, the Annales of the Central Meteorological Office at Rome, Bulletin of International Simultaneous Met. Obs. and the Monthly Weather Review of the Weather Bureau at Washington, the Abhandlungen of the Royal Prussian Meteorological Institute at Berlin, the Meteorological Papers of the Meteorological Office, London, and the transactions of numerous scientific societies, have represented the important official contributions of the respective national governments to technical meteorology. The recent international union for aerial exploration by kites and balloons has given rise to two important publications, i.e. the Veroffentlichungen of the International. Commission for Scientific Aerostatics (Strassburg, 1905, et seq.), devoted to records of observations, and the Beitrdge zur Physik der freien Atmosphdre (Strassburg, 1904, et seq.), devoted to research. The necessity of studying the atmosphere as a unit and of securing uniform accuracy in the observations has led to the formation of a permanent International Meteorological Committee (of which in 1909 the secretary was Professor Dr G. Hellmann of Berlin, and the president Dr W. N. Shaw of London). Under its directions conferences and general congresses have been held, beginning with that of 1872 at Leipzig. Its Inter-national Tables, Atlas of Clouds, Codex of Instructions, and Forms for Climatological Publications illustrate the activity and usefulness of this committee. Modern meteorology has been developed along two lines of study, based respectively on maps of monthly and annual averages and on daily weather maps. The latter study seems to have been begun by H. W. Brandes in Leipzig, who first, about 1820, compiled maps for 1783 from the data collected in the Ephemerides mannheimensis, and subsequently published maps of the European storms of 182o and 1821. Simultaneously with Brandes we find William C. Redfield in New Yorkcompiling a chart of the hurricane of 1821, which was published in 1831, and was the first of many memoirs by him on hurricanes that completely established their rotary and progressive motion. Soon after this Piddington and Sir William Reid began their great works on the storms of the Orient. About 1825 James Pollard Espy, in Philadelphia, began the publication of his views as to the motive power of thunderstorms and tornadoes, and in 1842 was appointed " meteorologist to the U.S. government " and assigned to work in the office of the surgeon-general of the army, where he prepared daily weather maps that were published in his four successive " Reports." In 1848 the three American leaders united in letters to Professor Joseph Henry, secretary of the Smithsonian Institution, urging that the telegraph be used for collecting data for daily maps and weather predictions. Favourable action was taken in 1849, the Smithsonian maps began to be compiled about 1851 and were displayed in public from 1853 onwards. Meanwhile in England James Glaisher, with the help of the daily press, carried out similar work, publishing his first map in 1851 as soon as daily weather maps of sufficient extent could be promptly prepared by the help of the telegraph. The destructive storm of the 14th of November 1854, in the Crimea gave U. J. J. Le Vervier, at Paris, an opportunity to propose the proper action, and his proposals were immediately adopted by the secretary of war, Marshal Valliant. On the 17th of February 1855 the emperor ordered the director-general of government telegraph lines to co-operate completely with Le Verrier in the organization of a bureau of telegraphic meteorology. The international daily bulletin of the Paris Observatory began to be printed in regular form on the 1st of January 1858, and the daily map of isobars was added to the text in the autumn of 1863. The further development of this bulletin, the inclusion of British and ocean reports in 186r, the addition of special storm warnings it1 1863, the publication of the Atlas des mauvements generaux covering the Atlantic in 1865, the study of local thunderstorms by Hippolyte Marie-Davy, Sonrel, Fron, Peslin, in France, and the work of Fitzroy, Buys-Ballot, Buchan, Glaisher and Thomson in Great Britain, parallel the analogous works of the American students of meteorology and form the beginnings of our modern dynamic meteorology. The details of the historical development of this subject are well given by Hugo Hildebrand-Hildebrandsson and Leon Teisserenc de Bort in their joint work, Les Bases de la meteorologie dynamique (Paris, 1898-1907). The technical material has been collected by Hann in his Lehrbuch. Many of the original memoirs have been reproduced by Brillouin in his Memoires originaux (Paris, 1900), and in Cleveland Abbe's Mechanics of the Earth's Atmosphere (vol. i., 1891; vol. ii., 1909). The publication of daily weather charts and forecasts is now carried on by all civilized nations. The list of government bureaux and their publications is given in Bartholomew's Atlas (vol. iii., London, 1899). Special establishments for the exploration of the upper atmospheric conditions are maintained at Paris, Berlin, Copenhagen, St Petersburg, Washington and Strassburg. The general problems of climatology (1900) are best presented in the Handbook of Dr Julius Hann (2nd ed., Stuttgart, 1897). The general distribution of temperature, winds and pressure over the whole globe was first given by Buchan in charts published by the Royal Society of Edinburgh in 1868, and again greatly revised and improved in the volume of the Challenger reports devoted to meteoro+ logy. The most complete atlas of meteorology is Buchan and Herbertson's vol. iii. of Bartholomew's Atlas (London, 1899). Extensive works of a more special character have been published by the London Meteorological Office, and the Deutsche Seewarte for the Atlantic, Pacific and Indian Oceans. Daily charts of atmospheric conditions of the whole northern hemisphere were published by the U.S. Weather Bureau from 1875 to 1883 inclusive, with monthly charts; the latter were continued through .1889. The physical problems of meteorology were discussed in Ferrel's Recent Advances in Meteorology (Washington, 1885). Mathematical papers on this subject will be found in the author's collection known as The Mechanics of the Earth's Atmosphere; the memoirs by Helmholtz and Von Bezold contained in this. collection have been made, the basis of a most important work by Brillouin (Paris, 1898), entitled Vents contigus et nuages. A general ,summary of our knowledge of the mechanics and physics of the atmosphere is contained in the Report on the International Cloud Work, by F. H. Bigelow (Washing-ton, 1900). The extensive Lehrbuch (Leipzig, 1901; 2nd ed., 1906) by Dr Julius Hann is an authoritative work. The optical phenomena of the atmosphere are well treated by E. Mascart in his Traite d'optique (Paris, 1891-1898), and by J. M. Penter, Meteorologische Optik (1904-1907). Of minor treatises especially adapted to collegiate courses of study we may mention those by Sprung (Berlin, 1885) ; W. Ferrel (New York, 1890) ; Angot (Paris, 1898) ; W. M.Davis, (Boston, 1893) ; Waldo (New York, 1898) ; Van Bebber (Stuttgart, 189o) ; Moore (London, 1893) ; T. Russell (New York), 1895. The brilliant volume by Svante Arrhenius, Kosmische Physik (Leipzig, 1900) contains a section by Sandstrom on meteorology, in which the new hydrodynamic methods of Bjerknes are developed. I.—FUNDAMENTAL PHYSICAL DATA There can be no proper study of meteorology without a consideration of the various physical properties of the atmospheric gases and vapours, each of which plays an independent part, and yet also reacts upon its neighbours. Atmospheric air is a mixture of nitrogen, oxygen, aqueous vapour, carbonic acid gas (carbon dioxide), ammonia, argon, neon, helium, with slight traces of free hydrogen and hydro-carbons. The proportions in which these gases are present are quite constant, except that the percentage of aqueous vapour is subject to large variations. In an atmosphere that is saturated at the temperature of 90° F., as may occur in such a climate as that of Calcutta, the water may be 240A of the whole weight of any given volume of air. When this aqueous vapour is entirely abstracted, the remaining dry gas is found to have a very uniform constitution in all regions and at all altitudes where examination has been carried out. In this so-called dry atmosphere the relative weights are about as follows: Oxygen, 23.16; nitrogen and argon, 76.77; carbonic acid, o•o4; ammonia and all other gases, less than o•oi in the lower half of the atmosphere but probably in larger percentages at great altitudes. Of still greater rarity are the highly volatile gases, argon (q.v.), neon, krypton and helium (q.v.). Outer Limit.—These exceedingly volatile components of the atmosphere cannot apparently be held down to the earth by the attraction of gravitation, but are continually diffusing through the atmosphere outwards into interstellar space, and possibly also from that region back into the atmosphere. There are doubtless other volatile gases filling interstellar space and occasionally entering into the atmosphere of the various planets as well as of the sun itself ; possibly the hydrogen and hydro-carbons that escape from the earth into the lower atmosphere ascend to regions inaccessible to man and slowly diffuse into the outer space. The laws of diffusion show that for each gas there is an altitude at which as many molecules diffuse inwards as outwards in a unit of time. This condition defines the outer limit of each particular gaseous atmosphere, so that we must not imagine the atmosphere of the earth to have any general boundary. The only intimation we have as to the presence of gases far above the surface of the globe come from the phenomena of the Aurora, the refraction of light, the morning and evening twilight, and especially from the shooting stars which suddenly become luminous when they pass into what we call our atmosphere. (See C. C. Trowbridge, ' On Luminous Meteor Trains " and " On Movements of the Atmosphere at Very Great Heights," Monthly Weather Review, Sept. 1907.) Such observations are supposed to show that there is an appreciable quantity of gas at the height of, loo m., where it may have a density of a millionth part of that which prevails at the earth's surface. Such matter is not a gas in the ordinary use of that term, but is a collection of particles moving independently of each other under those influences that emanate from sun and earth, which we call radiant energy. According to Stormer this radiant energy is that of electrons from the sun, and their movements in the magnetic field surrounding the earth give rise to our auroral phenomena. According to Professor E. W. Morley, of Cleveland, Ohio, the relative proportions of oxygen and nitrogen vary slightly at the surface of the earth according as the areas of high pressure and low pressure alternately pass over the point of observation; his remarkably exact work seems to show a possible variation of a small fraction of i %, and he suggests that the air descending within the areas of high pressure is probably slightly poorer in oxygen. The proportion of carbonic acid gas varies appreciably with the exposure of the region to the wind, increasing in proportion to the amount of the shelter; it is greater over the land than over the sea, and it also slightly increases by night-time as compared with day, and in the summer and winter as compared with the spring and autumn months. During the year 1896 Professor S. Arrhenius in the Phil. Mag., and in 1899 Professor T. C. Chamberlin in the Amer. Geol. Jour., published memoirs in which they argued that a variation of several per cent. in the proportion of carbonic acid gas is quite consistent with the existence of animal and vegetable life and may explain the variations of climate during geological periods. But the specific absorption of this gas for solar radiations is too small (C. G. Abbot, 1903) tosupport this argument. The question whether free ozone exists in the atmosphere is still debated, but there seems to be no satisfactory evidence of its presence, except possibly for a few minutes in the neighbourhood of, and immediately after, a discharge of lightning. The general proportions of the principal gases up to considerable altitudes can be calculated with close approximation by assuming a quiescent atmosphere and the ordinary laws of diffusion and elastic pressure; on the other hand, actual observations show that the rapid convection going on in the atmosphere changes these proportions and brings about a fairly uniform percentage of oxygen, nitrogen and carbonic acid gas up to a height of io m. Aqueous Vapours.—The distribution of aqueous vapour is controlled by temperature quite as much as by convection and has very little to do with diffusion; the law of its distribution in altitude has been well expressed by Hann by the simple formula: log e = log eo—h/6517 where h is the height expressed in metres and e and eo are the vapour pressures at the upper station and sea-level respectively. Hann's formula applies especially to observations made on mountains, but R. J. Suring, Wissenschaftliche Luftfahrten, III. (Berlin, 1900) has deduced from balloon observations the following formula for the free air over Europe log a=log eo—h(I+k/20000)/6000. He has also computed the specific moisture of the atmosphere or the mixing ratio, or the number of grams of moisture mixed with I kilogram of dry air for which he finds the formula log m=log mo-h(i+3h/4o)/9000. The relative humidity varies with altitude so irregularly that it cannot be expressed by any simple formula. The computed values of e and m are as given in the following table: Altitude Relative , Metres. Vapour Pressure. Relative h. a/eo. Specific Moisture. m/mo. O I000 I0o0 m 665 26 759 2000 oo 6 555 3000 158 264 4000 91 172 5000 5o Io8 6000 27 65 7000 14 38 8000 In addition to the gases and vapours in the atmosphere, the motes of dust and the aqueous particles that constitute cloud, fog and haze are also important. As all these float in the air, slowly descending, but resisted by the viscosity of the atmosphere, their whole weight is added to the atmosphere and becomes a part of thebarometric record. When the air is cooled to the dew-point and condensation of the vapour begins, it takes place first upon the atoms of dust as nuclei; consequently, air that is free from dust is scarcely to be found except within a mass of cloud or fog. Mass.—According to a calculation published in the U.S. Monthly Weather Review for February 1899, the total mass of the atmosphere is 1/1,I25,000 of the mass of the earth itself but, according to Professor R. S. Woodward (see Science for Jan. 1900), celestial dynamics shows that there may possibly be a gaseous envelope whose weight is not felt at the earth's surface, since it is held in dynamic equilibrium above the atmosphere; the mass of this outer atmosphere cannot exceed 216ath of the mass of the earth, and is probably far less, if indeed it be at all appreciable. Conductivity.—Dry air is a poor conductor of heat, its co-efficient of conduction being expressed by the formula: o•000 0568 (1-+-0.00190 t) where the temperature (t) is expressed in centigrade degrees. This formula states the fact that a plate of air i centimetre thick can conduct through its substance for every square centimetre of its area, in one second of time, when the difference of temperature between two faces of the plate is I° C., enough heat to warm i gram of water 0.000 0568° C., or I gram of air o•000 239° C., or a cubic centimetre of air o. 1850° C., if that air is at the standard density for 76o millimetres of pressure and 0° C. The figure 0.1850° C. is the thermometric coefficient as distinguished from the first or calorimetric coefficient (o.000 0568° C.), and shows what great effect on the air itself its poor conductivity may have. Diathermancy.—Dry air is extremely diathcrmanous or transparent., to the transmission of radiant heat. For the whole moist atmosphere the general coefficient of transmission increases as the waves become longer: and for a zenithal sun it is about 0.4 at the violet end of the spectrum and about o•8 at the red. By specific absorption many specific wave-lengths- are entirely cut off by the vapours and gases, so that in general the atmosphere may appearto be more transparent to the short wave-lengths or violet end of the spectrum, but this is not really so. When the zenithal sun's rays fall upon a station whose barometric pressure is 76o mm., then only from 5o to 8o% of the total heat reaches the earth's surface, and thus the general coefficient of transmission for the thickness of one atmosphere is usually estimated at about 6o %. Of course when the rays are more oblique, or when haze, dust or cloud interfere, the transmission is still further diminished. In general one half of the heat received from the sun by the illuminated terrestrial hemisphere is absorbed by the clearest atmosphere, leaving the other half to reach the surface of the ground, provided there be no intercepting clouds. The thermal conditions actually observed at the immediate surface of the globe during hazy and cloudy weather are therefore of minor importance in the mechanism of the whole atmosphere, as compared with the influence of the heat retained within its mass. The transmission of solar radiation through the earth's atmosphere is the fundamental problem of meteorology, and has been the subject of many studies, beginning with J. H. Lambert and P. Bouguer. The pyrheliometer of C. S. M. Pouillet gave us our first idea of the thermal equivalent of solar radiation outside of our atmosphere or the so-called " solar constant," the value of which has been variously placed at from 2 to 4 calories per sq. cm. per minute. At present the weight of the argument is in favour of 2.1, with a fair presumption that both the intensity and the quality of the solar radiation as it strikes the upper layers of our atmosphere are slightly variable. It is also likely that this " constant " does not represent the sun proper, but the remaining energy after the sunbeam has sifted through masses of matter between the sun and our upper atmosphere, so that it may thus come to have appreciable variations. The coefficients of absorption for specific wave-lengths were first determined by L. E. Jewell, of Johns Hopkins University, for numerous vapour lines in 1892 (see W. B. Bulletin, No. i6). In 1904 C. G. Abbot published a table based on bolograph work at Washington showing the coefficient of atmospheric transmission for solar rays passing through a unit mass of air-namely, from the zenith to the ground. He showed that this coefficient increased with the wave-length; hence any change in the quality of the solar radiation will affect the general coefficient of transmission. The following table gives his averages for the respective wave-lengths, as deduced from ten clear days in 1901-1902 and nine clear days in 1903:- Wave Length. Coefficient of Atmospheric Transmission (Abbot). 1901-1902. 1903. Mean by Weights. microns. - 0.484 - 0.40 violet 0.45 - 0.557 - o•50 0.765 0.627 0.700 o•6o 0.769 0.692 0.730 0.70 0.857 0.753 0.808 0.80 red 0.897 0.797 0.847 0.90 0.910 0.825 0.856 1.00 0.921 0.847 0.884 I.20 0.933 0.874 0.903 1.6o 0.930 0.909 0.920 2.00 0.950 0.912 0.919 Any variation in the energy that the atmosphere receives from the sun will have a corresponding influence on meteorological phenomena. Such variations were simultaneously announced in 1903 by Charles Dufour in Switzerland and H. H. Kimball in Washington (Monthly Weather Review, May 1903) ; the latter was then conducting a series of observations with Angstrom's electric compensation pyrheliometer, and his conclusions have been confirmed by the work of L. Gorczynski at Prague (1901-1906) and C. G. Abbot at Washington. Kimball's pyrheliometric work on this problem is still being continued; but meanwhile Abbot and Fowle from their bolometric observations at the Smithsonian Astrophysical Observatory have deduced preliminary values of the observed total energy, or the solar constant, for numerous dates when the sky was very clear, as follows (see Smithsonian Mis. Coll., xlv. 78 and xlvii. 403, 1905) :- Date. Abbot. Fowle. Calories. Calories. 1902 Oct. 9 2.19 2' 19 „ 15 2.19 - 22 2.16 1903 Feb . 19 2.28 2.27 „ 19 2.25 - March 3 2.26 - „ 25 2.27 2.23 26 2.10 - , 26 2.07 2.09 „ April17 1'99 t8 1, 1, 28 2.27 - 29 1.97 I.96 „ July 7 2.14 Oct. 14 - P96 „ Dec. 7 - 1.94 23 - 1'99 1904 Jan. 27 - 2.02 „ Feb. 11 - 2.26 „ May 28 - 2.09 „ Oct. 5 - 2.32 „ Nov. 16 1.98 If the relative accuracy of these figures is i %, as estimated by Abbot, then they demonstrate irregular fluctations of 5 %. But different observers and localities vary so much that Abbot estimates the reliability of the mean value, 2.12, to be about io%. The causes of this variation apparently lie above our lower atmosphere and move slowly eastward from day to day, and as the variability is comparable with that of other atmospheric data, therefore conservative meteorologists at present confine their attention to the explanation of terrestrial phenomena under the assumption of a constant solar radiation. The large local changes of weather and climate are not due to changes in the sun, but to the mechanical and thermodynamic interactions of earth and ocean and atmosphere. Excellent illustrations of this principle are found in the studies of Blanford, Eliot and Walker on the monsoons of India, of Sieger (1892) on the contrasts of temperature between Europe and North America, of Hann (1904) on the anomalies of weather in Iceland, of Meinardus (1906) on periodical variations of the icedrift near Iceland. The absorption of solar radiation by the atmosphere is apparently explained by the laws of diffuse reflection, selective diffusion and fluorescence in accordance with which each atom and molecule and particle becomes a new centre for the diffusion in all directions of the energy represented by some specific wave-length. The specific influences of carbon dioxide and water vapour are less than those of the liquid particles (and of cloud and rains) and of the great mass of oxygen and nitrogen that make up the atmosphere. Specific Heat.-The capacity of dry air for heat varies according as the heat increases the volume of the air expanding under constant vessure, or the pressure of the air confined in constant volume. he specific heat under constant pressure is about 1.4025 times the specific heat under constant volume. The numerical value of the specific heat under constant pressure is about 0.2375-that is to say, that number of gram-calories, or units of heat, is required to change the temperature of i gram of air by I ° C. This coefficient holds good, strictly speaking, between the temperatures-30° and +io° C., and there is a very slight diminution for higher temperatures up to 200°. The specific heat of moist air is larger than that of dry air, and is given by the expression C5" = (0.2375 + 0'4805 x) where x is the number of kilograms of vapour associated with I kilogram of dry air. As x does not exceed 0.030 (or 30 grams) the value of C,,", may increase up to 0.2519. The latent heat evolved in the condensation of this moisture is a matter of great importance in the formation of cloud and rain. Radiating Power.-The radiating power of clean dry air is so small that it cannot be measured quantitatively, but the spectroscope and bolometer demonstrate its existence. The coefficient of radiation of the moisture diffused in the atmosphere is combined with that of the particles of dust and cloud, and is nearly equal to that of an equal surface of lamp-black. From the normal diurnal change in temperature at high and low stations, it should be possible to deter-mine the general coefficient of atmospheric radiation for the average condition of the air in so far as this is not obscured by the influence of the winds. This was first done by J. Maurer in 1885, who obtained a result in calories that may be expressed as follows: the total radiation in twenty-four hours of a unit mass of average dusty'and moist air towards an enclosure whose temperature is 1 ° lower is sufficient to lower the temperature of the radiating air by 3.31 ° C. in twenty-four hours. This very small quantity was confirmed by the studies of Trabert, published in 1892, who found that 1 gram of air at 278° absolute temperature radiates 0.1655 calories per minute toward a black surface at the absolute zero. The direct observations of C. C. Hutchins on dry dusty air, as published in 189o, gave a much larger value-evidently too large. Slight changes in water, vapour and carbon dioxide affect the radiation greatly. The investigation of this subject prosecuted by Professor F. W. Very at the Allegheny Observatory, and published as " Bulletin G of the U.S. Weather Bureau, shows the character and amount of the radiation of several gases, and especially the details of the process going on under normal conditions in the atmosphere. Density.-The absolute density or mass of a cubic centimetre of dry air at the standard pressure, 76o millimetres, and temperature 0° C., is 0.001 29305 grams; that of a cubic metre is 1.29305 kilograms; that of a cubic foot is o.o8o7i lb avoirdupois. The variations of this density with pressure, temperature, moisture and gravity are given in the Smithsonian meteorological tables, and give rise to all the movements of the atmosphere; they are, therefore,.of fundamental importance to dynamic meteorology. Expansion.-The air expands with heat, and the expansion of aqueous vapour is so nearly the same as that of -dry air that the same coefficient may be used for the complex atmosphere itself. The change of volume may be expressed in centigrade degrees by the formula V=V0 (i+o•000 3665t), or in Fahrenheit degrees V=Vo (1+0.000 237t). Elasticity.-The air is compressed nearly in proportion to the pressure that confines it. The pressure, temperature and volume of the ideal gas are connected by the equation pv = RT, where T is the absolute temperature or 273° plus the centigrade temperature p is the barometric pressure in millimetres and v the volume of a unit mass of gas, or the reciprocal of the density of the gas. The constant R is 29.272 for dry atmospheric air when the centimetre, the gram, the second and the centigrade degrees are adopted as units of measure, and differs for each gas. For aqueous vapour in a gaseous state and not near the point of condensation R has the value 47.061. For ordinary air in which x is the mass of the aqueous vapour that is mixed with the unit mass of dry air, the above equation becomes pv=(29.272+47.061x) T. This equation is sometimes known as the equation of condition peculiar to the gaseous state. It may also be properly called the equation of elasticity or the elastic equation for gases, as expressing the fact that the elastic pressure p depends upon the temperature and the volume. The mose exact equations given by Van der Waals, Clausius, Thiesen, are not needed by us for the pressures that occur in meteorology. Diffusion.—In comparison with the convective actions of the winds, it may be said that it is difficult for aqueous vapour to diffuse in the air. In fact, the distribution of moisture is carried on principally by the horizontal convection due to the wind and the vertical convection due to ascending and descending currents. Diffusion proper, however, comes into play in the first moments of the process of evaporation. The coefficient of diffusion for aqueous vapour from a pure water surface into the atmosphere is 0.18 according to Stefan, or 0.1980 according to Winkelmann; that is to say, for a unit surface of 1 sq. centimetre, and a unit gradient of vapour pressure of one atmosphere per centimetre, as we proceed from the water surface into the still dry air, at the standard pressure and temperature, and quantity of moisture diffused is 0.198o grams per second. This coefficient increases with the temperature, and is 0.2827 at 49.5° C. But the gradient. of vapour pressure, and therefore rate of diffusion, diminishes very rapidly at a small distance from the free surface of the water, so that the most important condition facilitating evaporation is the action of the wind. Viscosity.—When the atmosphere is in motion each layer is a drag upon the adjacent one that moves a little faster than it does. This drag is the so-called molecular or internal friction or viscosity. The coefficient of viscosity in gases increases with the absolute temperature, and its value is given by an equation like the following; 0.000 248 (1+o•ooe 6651) which is the formula given by Carl Barus (Ann. Phvs., 1889, xxxvi.). This expression implies that for air whose temperature is the absolute zero there is no viscosity, but that at a temperature (t) of 0° C., or 2730 on the absolute scale, a force of 0.000 248 grams is required in order to push or pull a layer of air t centimetre square past another layer distant from it by 1 centimetre at a uniform rate oft centimetre per second. Friction.—The general motions of the atmosphere are opposed by the viscosity of the air as a resisting force, but this is an exceedingly feeble resistance as compared with the obstacles encountered on the earth's surface and the inertia of the rising and falling masses of warm and cold air. The coefficient of friction used in meteorology is deduced from the observations of the winds and results essentially not from viscosity, but from the resistances of all kinds to which the motion of the atmosphere is subjected. The greater part of these resistances consists essentially in a dissipation of the energy of the moving masses by their division into smaller masses which penetrate the quiet air in all directions. The loss of energy due to this process and the conversion of kinetic into potential energy or pressure, if it must be called friction, should perhaps be called convective friction, or, more properly, convective-resistance. The coefficient of resistance for the free air was determined by Mohn and Ferrel by the following considerations. When the winds, temperatures and barometric .pressures are steady for a considerable time, as in the trade winds, monsoons and stationary cyclones, it is the barometric gradient that overcomes the resistances, while the resulting wind is deflected to the right (in the northern hemisphere) by the influence of the centrifugal force of the diurnal rotation (co) of the earth. The wind, therefore, makes a constant angle (a) with the direction of the gradient (G). There is also a slight centrifugal force to be considered if the winds, are circulating with velocity v and radius (r) about a storm centre, but neglecting this we have approximately for the latitude G sin a = 2ccv sin G cos a = Kv, where (K) is the coefficient connecting the wind-velocity (v) with the component of the gradient pressure in the direction of the wind. These relations give K = 2w sin 0/tan a. The values of a and v as read off from the map of winds and isotherms at sea level give us the data for computing the coefficients for oceanic and continental surfaces respectively, expressed in the same units as those used for G and v. The extreme values of this coefficient of friction were found by Guldberg and Mohn to be 0.00002 for the free ocean and 0.00012 for the irregular surface of the land. For Norwegian land stations Mohn found = 61° a = 56.5° K = 0.0000845. For the interior of North America Elias Loomis found ¢ = 37.5° a = 42.2 ° = o•00008o3. Gravity.—The weight of the atmosphere depends primarily upon the action of gravity, which gives a downward pressure to every particle. Owing to the elastic compressibility of the air, this downward pressure is converted at once into an elastic oressurein all directions. The force of gravity varies with the latitude and the altitude, and in any exact work its variations must be taken into account. Its value is well represented by the formula due to Helmert, g = 980.6 (1 — o•0026 cos 2¢) X (1 — fh), where 4 represents the latitude of the station and h the altitude. The coefficient f is small and has a different value according as the station is raised above the earth's surface by a continent, as, for instance, on a mountain top, or by the ocean, as on a ship sailing over the sea, or in the free air, as in a balloon. Its different values are sufficiently well known for meteorological needs, and are utilized most discreetly in the elaborate discussion of the hypsometric formula published by Angot in 1899 in the memoirs of the Central Meteorological Bureau of France. Temperature at Sea-Level.—The temperature of the air at the surfaces of the earth and ocean and throughout the atmosphere is the fundamental element of dynamic meteorology. It is best exhibited by means of isotherms or lines of equal temperature drawn on charts of the globe for a series of level surfaces at or above sea-level. It can also be expressed analytically by spherical harmonic functions, as was first done by Schoch. The normal distribution of atmospheric temperature for each month of the year over the whole globe was first given by Buchan in his charts of 1868 and of 1888 (see also the U.S. Weather Bureau " Bulletin A," of 1893, and Buchan's edition of Bartholomew's Physical Atlas, London, 1899). The temperatures, as thus charted, have been corrected so as to represent a uniform special set of years and the conditions at sea-level, in order to constitute a homogeneous system. The actual temperature near the ground at any altitude on a continent or island may be obtained from these charts by subtracting 0.5°C. for each too metres of elevation of the ground above sea-level, or 1° F. for 35o ft. This reduction, however, applies specifically to temperatures observed near the surface of the ground, and cannot be used with any confidence to determine the temperature of points in the free air at any distance above the land or ocean. On all such charts the reader will notice the high temperatures near the ground in the interior of each of the continents in the summer season and the low temperatures in the winter season. In February the average temperatures in the northern hemisphere are not lowest near the North Pole, but in the interiors of Siberia and North America; in the southern hemisphere they are at the same time highest in Australia, and Africa and South America. In August the average temperatures are unexpectedly high in the interior of Asia and North America, but low in Australia and Africa. Temperature at Upper Levels.—The vertical distribution of temperature and moisture in the free air must be studied in detail in order to understand both the general and the special systems of circulation that characterize the earth's atmosphere. Many observations on mountains and in balloons were made during the 19th century in order to ascertain the facts with regard to the decrease of temperature as we ascend in the atmosphere; but it is now recognized that these observations were largely affected by local influences due to the insufficient ventilation of the thermometers and the nearness of the ground and the balloon. Strenuous efforts are being directed to the elimination of these disturbing elements, and to the continuous recording of the temperature of the free air by means of delicate thermographs carried up to great heights by small free "sounding balloons," and to lesser heights by means of kites. Many international balloon ascents have been made since 189o, and a large amount of information has been secured. The development of kite-work in the United States began in October 1893, at the World's Columbian Congress at Chicago, when Professor M. W. Harrington ordered Professor C. F. Marvin of the Weather Bureau to take up the development of the Hargrave or box kite for meteorological work. At that time W. A. Eddy of Bayonne, New Jersey, was applying his " Malay kite to raising and displaying heavy objects, and in August 1894 (at the suggestion of Professor Cleveland Abbe) he visited the private observatory of A. L. Rotch at Blue Hill and demonstrated the value of his Malay kite for aerial research. The first work done at this observatory with crude apparatus was rapidly improved upon, while at the same time Professor Marvin at Washington was developing the Hargrave kite and auxiliary apparatus, which he brought up to the point of maximum efficiency and trustworthiness. When he reported his apparatus as ready to be used by the Weather Bureau on a large scale, Professor Willis L. Moore, as the successor of Professor Har= rington, ordered its actual use at seventeen kite stations in July 1898. This was the first attempt to prepare isotherms fora special hour over a large area at some high level, such as t m., in the free air. Daily meteorological charts were prepared for the region covered by these observations; but it became necessary to discontinue them, and nothing more was done by the Weather Bureau in this line of work until the inauguration of kite work at Mount Weather in 1906. Meanwhile a special method for the reduction and study of such observations was devised by Bjerknes and Sandstrom, and was published in the Trans. American Philosophical Society (Philadelphia, 1906). The general average results as to temperature gradients were compiled by Dr H. C. Frankenfield and published 19 the United States Weather Bureau " Bulletin F.". from twee. were deduced the following tables, published in the Monthly Weather Review:- Mean Temperature Gradients in degrees Fahrenheit per zoo° ft. from the ground up to the respective altitudes. Stations. Il000 1500 2000 3000 4000 5000 6000 ft. ft. ft. ft. ft. ft. ft. 0 0 0 0 0 0 0 Washington, D.C. . . 5.6 4.4 4'0 3.5 3.2 3'0 3.1 Cairo, Ill. . . . 9.7 6.6 6•o 4.9 4.7 4.3 - Cincinnati, O. . . . 13.0 6.3 6.9 5'8 5'6 4.7 4'2 Fort Smith, Ark. . . 7.2 7.0 6.7 5.8 3.8 - Knoxville, Tenn. . . 8.4 6.2 6.6 5'4 5'0 - - Memphis, Tenn. . . 7.8 6.8 5.0 3.8 3'7 3.5 Springfield, Ill. . . . 7.6 5.7 5•I 4.4 4.0 3.7 3.6 Cleveland, O. . . . 5'7 4.1 3.6 3'5 4.1 4'I 4.3 Duluth, Minn. . . . 5'2 4.8 4.6 4'6 4.3 3.8 4.6 Lansing, Mich. . . 7.5 6•o 4.7 4.1 3.9 3'8 - Sault Ste Marie, Mich. . 6.6 6.2 5.2 4'5 3'9 3'0 - Dodge, Kans. . . . 6.3 5.2 4.8 3.7 3.1 3.2 3.2 Dubuque, Iowa . . 6.9 5.9 4.6 3'5 3.2 3.3 - North Platte, Neb. . . 6.8 6.5 5.9 5'2 4'4 4.7 5.4 Omaha, Neb. . . . - 5.4 4.9 3'6 3.2 3'5 3.8 Pierre, S. Dak. . . . 5.9 5.1 4'8 4.3 3'7 4.4 4.0 Topeka, Kans. . . . 7.4 6.2 4.9 4.0 3.8 3.9 4.5 Average . . . . 7.4 5.8 5'2 4'4 4.0 3'8 4.1 Stations Altitude. Temperature. Feet. Gradient. Reduction. °F. °F. Washington 210 -3.00 -15.2 Cairo 315 -4'30 -25.6 Cincinnati 940 -5'15 -27.5 Fort Smith 527 ? ? Knoxville 990 -5'00 -21.5 Memphis 319 -3.50 -17'3 Springfield 684 -3'85 -17'7 Cleveland 705 -4.10 -18.8 Duluth 1197 -4'30 -17.6 Lansing 869 -3'85 -17.0 Sault Ste Marie 722 -3'45 -15'7 Dodge 2473 -4'10 -11.6 North Platte 2891I -5.40 -13.3 Omaha I241 -3.20 -12.9 Topeka 977 192 -33.'8 3 3 -16.4 5 In this table the second column gives the altitude of the ground at the reel on which the kite wire was wound. The third column shows the average gradient in degrees Fahrenheit. per moo ft. between the reel at the respective stations, and a uniform altitude 528o ft. above sea-level. The fourth column shows the total reduction to be applied to the temperature at the reel in order to obtain the temperature at the 1 m. level above sea. These gradients and reductions are based upon observations made only during the six warm months from May to October 1898. The kite-work at the Blue Hill Observatory has been published in full in the successive Annals of the Harvard College Observatory, beginning with 1897, vol. xlii. It has been discussed especially by H. H. Clayton with reference to special meteorological phenomena, such as areas of high and low pressure, fair and cloudy weather, the winds and their velocities at different elevations, insolation, radiation, &c., and has served as a stimulus and model for European meteorologists. Kite-work has also been successfully prosecuted at Trappes, Hamburg, Berlin, St Petersburg, and many other European stations. The highest flights that have been attained have been about 8000 metres. The great work of L. Teisserenc de Bort began with 1897, when he founded his private observatory at Trappes near Paris devoted to the problems of dynamic meteorology. His results are published in full in the Memoirs of the Central Meteorological Bureau of France for 1897 and subsequent years. Beginning with the sounding balloons devised by Hermite, he subsequently added kite work as supplementary to these. In the Corn pies rendus (1904), he gives the mean temperatures as they result from five years of work, 1899-1903, at Trappes. Out of 581 ascensions of sounding balloons there were 141 that attained 14 km. or more, and the following table gives the average temperatures recorded in these ascensions. It will be seen that there is a slow decrease in temperate up to 2 km.; a rapid decrease thence up to to km., and a slow decrease, almost a stationary temperature, between11 and 14 km.; this is the " thermal zone " as discovered and so called by him. Altitude. Winter. Spring. Summer. Autumn. Dec., Jan., Feb. Mar., Apt., May. June, July, Aug. Sept., Oct., Nov. Km. °C. °C. °C. °C. Ground + 1.9 + 5.1 +13'0 + 7'5 0.5 + 1.4 + 4' 7 +13'6 + 7' 7 I•o - 0.2 + 2.4 +I1.8 + 6•I I .5 - 0.2 + 0.1 9.7 + 4.0 2 .0 - 1.4 - 2.1 7.3 + 2.2 2'5 - 3.7 - 4.3 5.0 + 0'4 3.0 - 6•o - 6.4 2•I - P7 3'5 -8.7 -9.3 -1-0.2 -4.2 4'0 - 10.9 - 12.2 - 2'7 - 6.5 4'5 - 14.2 - 15.2 - 5.3 - 9'3 5.0 -17.0 -18.5 - 8.3 -12.4 6•o -23.7 -25.2 -14'8 -18'7 7.0 -31.5 -32.0 -21.7 -25.8 8.0 -39'0 -39'0 -29'3 _33'5 9.0 -46.9 -46.7 -38.0 -41.4 Io•o -54'6 -52'7 45'3 -48'3 I I.0 -57.9 -53'6 50.3 -54'4 12.0 -57.9 -53.1 52.7 -57.1 13.0 -56.9 -52°2 51'5 -57.1 14.0 -55.5 -52.5 -51'3 -57'1 It is evident that the annual average vertical gradient of temperature over Paris is between 40 and 6° C. per moo metres of ascent in the free air, agreeing closely with the value 5° per I000 metres, which has come into extensive use since the year 189o, on the recommendation and authority of Hann, for the reduction of land observations to sea-level. The winter gradients are less than those for summer, possibly owing to the influence of the condensation into cloud and rain during the winter season in France; the same value may not result from observations in the United States, where the clouds and precipitation of winter do not so greatly exceed those of summer. The work at Trappes is therefore not necessarily representative of the general average of the northern hemisphere, but belongs to a coastal region in which during the summer time, at great heights, the air is cooler than in the winter time, since during the latter season there is an extensive flow of warm south winds from the ocean over the cold east winds from the land. Sounding balloons have also been used elsewhere with great success. The greatest heights attained by them have been 25,989 metres at Uccle, Belgium, on the 5th of September 1907, and 25,800 metres at Strassburg, August 1905. The most extensive meteorological explorations of the free atmosphere have been those accomplished in Germany by Richard Assmann and Arthur Berson, beginning (1887) in co-operation with the German Verein for the Promotion of Aeronautics and the Aeronautic Section of the German Army, afterwards under the auspices of the Prussian Meteorological Office,. but later as a wholly independent institution at Lindenberg. ll the details of the work during 1887-1889 and the scientific results of seventy balloon voyages were published in three large volumes, Wissenschaftliche Luftschiffahrten (Berlin, 1900). The work done at Tegel at the Aeronautical Observatory of the Berlin Meteorological Office, the 1st of October 1899 to April 1905, was published in three volumes of Ergebnisse. But the location at Tegel had to be given up and a new independent establishment, the " Royal Prussian Aeronai iic Observatory," was founded at Lindenberg, under the direction of Dr Assmann, who has published the results of his work in annual volumes of the Ergebnisse of that institution, considering it as a continuation of the work done at Berlin and Tegel. In addition to these elaborate official publications various summaries have been published, the most instructive of which is the chart embodying daily observations .with corresponding isotherms at all attainable altitudes, published monthly since January 1903 in Das Wetter. The growth of this aerial work and the reliability of the results may be inferred from a statement of the number of ascensions made each year: 1899, 6; 1900' 39; 190I, 169; 1902, 261; 1903, 481; 1905, 513. This large number, combined with 581 voyages of Teisserenc de Bort at Trappes and many others made in England, Annual Temperatures and Wind. Tegel, 1903. Tegel, 1904. Lindenberg, 1905. Lindenberg, 1905. Altitude. Days. °C. Days. °C. Days. Sc. Days. Metres per sec. Ground 365 9.2 366 9.1 365 8.5 365 4.65 500 M. 363 6.7 364 6.5 365 6.2 362 8.65 1,000 ,, 344 4'3 361 4'2 352 4.0 356 8.85 1,500 ,, 252 2.0 279 2.2 294 2.6 306 8'55 2,000 ,, 170 0.0 186 -0.2 242 0.5 257 9.5 2,500 „ 98 - I.8 132 - 1.7 179 - I•I 195 10.0 3,000 ,, 55 -3'9 79 -3'6 119 -2.8 127 Io•7 Holland and Russia, amounting in all to over 2000, enabled Assmann to compute the monthly and annual means of temperature and wind velocity for each altitude; the German results are given in table at foot of page 269. The results of these numerous ascents, during these six years, have also been grouped into monthly means that have a reliability proportionate to the number of days on which observations were obtained at a given level, and we are now able to speak of the annual and even of the diurnal periodicity of temperature at different altitudes in the free air with considerable confidence. Some of the most important conclusions to be drawn from the best recent work were published by Hann either in special memoirs or in his Lehrbuch, from which we take the following table. The actual temperatures given in this table have only local importance, but the differences or the vertical gradients doubtless hold good over a large portion of Europe if not of the world. The differences of temperature between any layer and those above it and below it, or the vertical gradients at each level go through annual periodical changes quite analogous to those derived from mountain observations; the most rapid falls of temperature, or the largest vertical gradients in the free air occur on the following dates over Europe: Altitude. Over Over Germany. Trappes. I, 2, 3 km. May, June May 15 3, 4 5 March Feb. 15 5, 6, 7 April Jan. 27 7, 8, 9 July July 28 9, 10, II - Sept. 14 The values above given as deduced from ial.high ascensions at Trappes show that between 11 and 14 km. there was no appreciable diminution of temperature, in other words, the air is warmer than could be expected and therefore has a higher potential temperature. This fact was first confirmed by the Berlin ascensions, and is now recognized as wellnigh universal. The altitude of the base of this warm stratum is about 12 km. in areas of high pressure and Io km. in areas of low pressure. It is higher as we approach the tropics and above ordinary balloon work near the equator if indeed it exists there. At first this unexpected warmth was considered the highest cirrus, from which Cleveland Abbe inferred that it had something to do with the absorption of the solar and terrestrial heat by dissolving cirri. But the most plausible explanation is that published simultaneously in September 1908 by W. J. Humphreys of Washington, and Ernest Gold of London. The daily diagrams in Das Wetter show that both the irregular and the periodic and the geographic variations of temperature in the upper strata are unexpectedly large, almost as large as at the earth's surface, so that the uniform temperature of space that was formerly supposed to prevail in the upper air must be looked for, if at all, far above the level to which sounding balloons have as yet attained. It is evident that both horizontal and vertical convection currents of great importance really occur at these great altitudes. These upper currents cannot be due to any very . local influence at the earth's surface, but only to the interchange of the air over the oceans and continents or between the polar and equatorial regions. They constitute the important feature of the so-called general circulation of the atmosphere, which we have hitherto mistakenly thought of as confined to lower levels; their general direction is from west to east over all parts of the globe as far as yet known, showing that they are con-trolled by the rotation of the earth. It is likely that masses of air having special temperature conditions or clouds of vapour dust such as came from Krakatoa, may be carried in these high currents around the globe perhaps several times before being dissipated. The average eastward movement or the west wind at 3 km. above Germany is 10.7 M. per sec. or 1° of longitude (at 45° latitude) in 42'4 minutes, or such as to describe the whole circumference of this small circle in Io•5 days. At the equator above the calm belt the velocity westward or the east wind as given by Krakatoa volcanic-dust phenomena was 34'5 m per sec., on 30 of a great circle daily, or around the equator in 12.5 days, while its poleward movement was only I ° per day or 1.3 metre per second. The average motion of the storm centres moving westward in northern tropical and equatorial regions but eastward in the north temperate zone is at the rate of one circumference or a small circle at latitude 45° in 19 days. Observations of the cloud movements gave Professor Bigelow the following results for the United States: Altitude. Moving Moving eastward. westward. 1o•o km. 36 m. p.s. 2.0 M. p.s. 7.5 35 2.0 5.0 26 1.5 3•o 20 1 •o 1.0 8 - 0.5 0 4 Temperature in Free Air over Europe 1899-1904. Annual Averages. International. All Altitude. Inter- Manned countries Berlin. national. balloons. Trappes. Feb. Aug. combined. 15 Ascents. 130 Ascents. 36 Ascents. 581 Ascents. Km. ° C. 'c . ° C. ° C. ° C. ° C. ° C. o - 8 3 - - + o•3 +18.2 + 5.4 6'o + 5'5 + 5'3 - 1'4 + 15'1 5.0 2 + 0.5 1.7 + 0.3 + 0.7 - 3.6 +10.2 0.5 3 - 5.o - 3'3 - 4.4 -- 4.0 - 8.7 + 4.8 - 4.0 4 -10.3 - 9.0 -10.3 - 9.4 -14'7 - 1'0 - 9'2 5 -16.6 -15.3 -16.5 -15'4 -21.9 - 7.1 -15.4 6 -24.2 -22.1 -23•o -21.9 -28.9 -13.3 -22.0 7 -30.2 -29.1 -30.2 -29.0 -36.1 -19.5 -29.0 8 -37'4 -36.2 -37.0 -36.2 _43.7 -27.1 -36.2 9 -46'4 -43.2 - -43'5 -50.1 -33'8 -43.2 I0 - -49'0 - -49'3 -55'4 -39'5 -49'2 Evidently, therefore, the great west wind (that James H. Coffin deduced from' his work on the winds of the northern hemisphere and that William Ferrel deduced from his theoretical studies) repre- sents with its gentle movement poleward a factor of fundamental as possibly a matter of error in the meteorographs, but this idea is importance. We must consider all our meteorological phenomena now abandoned. Assmann suggested that the altitude is that of except at the equator as existing beneath and controlled, if not Average temperature gradient Altitude Total Fall of Temperature from Ground upward. per loo metres. Month. Altitudes. (metres). October to March. April to September. From o to From moo to Cloudiness Cloudiness Cloudiness Cloudiness moo metres. 2000 metres. 0-7. 8-1o. o-7. 8-ro. ° C. ° C. ° C. ° C. ° C. ° C. January o•11 o•58 2000 8.24 7.63 15.33 14'18 _ February 0'39 0.30 1800 7.22 6.6o 14.20 12.97 March 0.33 0 40 1600 6 28 6.04 13.01 I I.75 April 0 73 0 48 1400 5'35 5' 15 11.66 Io•59 May 0.90 o'66 1200 4'48 4'35 10.32 9'32 June 0.99 0.72 1000 3.62 3.52 9.13 7.96 July 0.96 o•67 800 2'20 2.82 7'55 6.65 August . ; o•86 o•62 600 1.54 2.33 5'77 5'23 September 0.77 0'58 400 o'65 1.85 3.88 3.63 October 0.57 0'43 200 0'35 1.05 1.88 1.76 November 0.36 0.53 0 0.00 0.00 0.00 0.00 December 0.30 0.53 _ _ Year o•61 o•53
End of Article: METEOROLOGY (Gr. JerEwpa, and hb'yos, i.e. the science of things in the air)

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