CLIMATE

INTRODUCTION

Meaning and Scope of Climatology-Relation of Meteorology and Climatology-Literature of Climatology-The Climatic Elements and their Treatment-Solar Climate-Physical Climate.

Meaning and Scope of Climatology. The word klima (from liver, to incline), as used by the Greeks, originally referred to the supposed slope of the earth toward the pole, or to the inclination of the earth's axis or of the sun's rays. It may, perhaps, have had reference to the different exposures of mountain slopes. Later, probably after Aristotle's time, it came to be used as about equivalent to our zone, but at first it was simply a mathematical or an astronomical term, not associated with any idea of physical climate. A change of latitude in those days meant a change of climate. Such a change was gradually seen to mean a change of atmospheric conditions as well as a change in length of day. Thus klima came to have its present meaning.

An excellent illustration of the ancient meaning of

the word klima is found in the system of climates proposed by the famous geographer, Ptolemy. This was a division of the earth's surface between equator and north pole into a series of climates, or parallel zones, separated by latitude circles and differing from one another simply in the length of their longest day. Ptolemy's subdivision of the earth's surface was really nothing but an astronomical climatic table.

Climate, as we use the term, is the resultant of the average atmospheric conditions, or, more simply, it is the average condition of the atmosphere. Weather is a single occurrence, or event, in the series of conditions which make up the climate. The climate of a place is in a sense its average weather. The average values of these atmospheric conditions can be determined only by means of careful observations, continued for a period sufficiently long to give accurate results. Climatology is the study or science of climates.

Relation of Meteorology and Climatology. Meteorology and climatology are interdependent. It is impossible to distinguish very sharply between them. Each needs the results obtained by the other. In a strict sense, meteorology deals with the physics of the atmosphere. It considers the various atmospheric phenomena individually, and seeks to determine their physical causes and relations. Its view is largely theoretical. The aspect of meteorology which is of most immediate practical importance to man is that which concerns weather-forecasting.

When the term meteorology is used in its broadest meaning, climatology is a subdivision of meteorology. Climatology is largely descriptive. It aims to give as clear a picture as possible of the interaction of the various atmospheric phenomena at any place on the earth's surface. It rests upon physics and geography, the latter being a very prominent factor. Climatology may almost be defined as geographical meteorology. Its main object is to be of practical service to man. Its method of treatment lays most emphasis on the elements which are of the most importance to life. Climate and crops, climate and industry, climate and health, are subjects of vital interest to man. No other science concerns man more closely in his daily life.

Literature of Climatology. Scientific climatology is based upon numerical results obtained by systematic, long-continued, and accurate meteorological observations. The essential part of its literature is therefore found in the collections of data published by the various meteorological services and observatories. In addition, large numbers of short sketches and notes on climate, partly the more or less haphazard accounts of travellers, partly the more careful studies of scientific observers, are scattered through a wide range of geographical and other publications. The only comprehensive text-book of climatology is the Handbuch der Klimatologie of Professor Julius Hann, of the University of Vienna. This is the standard book on the subject, and upon it is based

much of the present volume, and of other recent discussions of climate. The second edition of this work, in three volumes, was published in 1897 (Stuttgart, Engelhorn). The first volume deals with general climatology, and has been translated into English.1 The second and third volumes are devoted to the climates of the different countries of the world. Woeikof's Die Klimate der Erde (Jena, Costenoble, 1887) is also a valuable reference book. The first part concerns general relations of climate, particularly to rivers and lakes, to vegetation, and to snow-cover, while the second part deals with the climates of special areas. The standard meteorological journal of the world, the Meteorologische Zeitschrift (Braunschweig, Vieweg, monthly), is indispensable to anyone who wishes to keep in touch with the latest publications on climatology, for it contains the most complete record of such literature, as well as a large number of original notes and discussions. The newest and most complete collection of charts is that in the Atlas of Meteorology (London, Constable, 1899), in which also there is an excellent bibliography. For the titles of more recent publications reference may be made to the International Catalogue of Scientific Literature (annual volume on Meteorology); or to the more frequent bibliographical lists in the Meteorologische Zeitschrift; the Monthly Weather Review (Washington, U. S. Weather Bureau); the Quarterly Journal of

1By R. De C. Ward. London and New York, Macmillan, 1903.

the Royal Meteorological Society (London), and the Halbmonatliches Litteraturverzeichniss der "Fortschritte der Physik" (Braunschweig, Vieweg, twice a month).

The Climatic Elements and their Treatment. Climatology has to deal with the same groups of atmospheric conditions as those with which meteorology is concerned, viz.: temperature (including radiation); moisture (including humidity, precipitation, and cloudiness); wind (including storms); pressure; evaporation, and also, but of less importance, the composition and the chemical, optical, and electrical phenomena of the atmosphere. The characteristics of each of these so-called climatic elements are set forth in a standard series of numerical values, based on careful, systematic, and long-continued meteorological records, corrected and compared by wellknown methods. Various forms of graphic presentation, by curves, or by wind roses, etc., are employed to emphasise and simplify the numerical results. Instructions concerning the use, exposure, hours of observation, and corrections of the ordinary meteorological instruments; as well as for obtaining the usual numerical results, are published by the various governmental meteorological services. In Hann's Handbook of Climatology, Vol. I, will be found a general discussion of the methods of presenting the different climatic elements, and of the reasons for adopting the accepted scheme of presentation. The most complete guide in the numerical, mathematical,