CLIMATE (OF. climat, from Lat. clima, Gk. κλίμα, klima, region, slope, from κλίνειν, klinein, to incline). A word used in meteorology to indicate the summation or general result of all the solar and terrestrial influences that affect animal or vegetable life. It is possible, in fact, to disregard the relation to life, and consider only the meteorological phenomena as such, or the phenomena that affect any phase of our activity. Thus, one may ask, How does the climate favor navigation by sailing vessels, or the use of the wind as a motive power? In one region the climate may favor the development of a certain disease; in another, it may favor the development of special varieties of plants or animals. The specific features that favor the growth of either plants or animals, enabling them to make a specific spot their home, are oftentimes so obscure as to elude our observation and record; therefore, climatology is, in many respects, still an unsatisfactory study; but it has made such progress in the past fifty years as to have become exceedingly important to many classes of industries, as well as to physicians, naturalists, and agriculturists. Some varieties of plants are so dependent upon the nature of the soil in which they grow that Dr. Milton Whitney, of the United States Department of Agriculture, has advocated defining climatology as that which concerns the soil around the roots of the plant; but this is too narrow a view of the subject.
According to the usage of classic Greek, climate concerned principally the temperature of a place as regulated by the altitude of the sun at midday. As this varies with latitude, the ancients divided the known globe into zones two degrees broad in latitude, each of which was supposed to have its climate. At the present time, by combining the accumulated work of thousands of observers, we divide the globe into irregular regions, each of which differs from its neighbor in some important climatic condition as to temperature, rainfall, pressure, moisture, or the inclination of the sun and the amount of cloudiness. In the extensive works of the most eminent writers on climatology, especially those of Dr. Julius Hann, of Vienna, a large number of meteorological items are enumerated as being essential to a complete study of the climate of any place. These items include not merely the mean temperature, rainfall, cloudiness, the barometric pressure and relative humidity, but also the variations of these quantities, viz. their highest and lowest values each day, or month, or year, and the liability to sudden rises or falls. For navigation and the use of windmills, we need to know the average velocity of the wind, and perhaps especially the number of hours during which the wind exceeds a specified limit. With reference to the growth or importation of tender plants, the agriculturist needs to know the mean dates of the last frost of spring and the first frost of the autumn, the difference between which is ordinarily called the growing season. Since the establishment of the fact that the germination of seed, the growth of the plant, and the ripening of the harvest requires a certain amount of heat or molecular energy, efforts have been made to determine the thermal constants for many plants, and for each phase in growth. This ‘thermal constant’ is usually expressed as the sum total of the average daily temperatures when such temperatures are above 42° F. There is also a ‘rainfall constant’ peculiar to each species of plant, the nature of which has been investigated by Linsser, who has shown that plants are able, by gradual evolution, to change their own thermal and aqueous constants, and eventually adapt themselves to a change in climate. Linsser's laws serve as a guide to those who would transplant a species from one part of the world to another of different climate.
In the study of climate with reference to navigation, we have to consider the frequency of destructive storm-winds. Charts showing this factor have been published for all the oceans and seas by the hydrographic offices of England, France, Holland, Russia, and the United States. In addition to this, for the special benefit of sailing vessels, Galton has shown how to prepare charts showing, for each square degree, the progress that a vessel of a certain size and rig would make if her sails were set so that she should go in a certain direction. From the point of view of insurance, both life insurance and fire insurance, the destruction by wind, hail, and lightning have been studied; these data, being plotted on charts, show the climate of the country from that point of view. Perhaps the most general idea of the distribution of climate is given by charts which show the frequency per month or year with which storm-centres pass over a given locality, and the direction in which they pass. A map of such frequency for the eastern portion of the United States was first published in the Statistical Atlas of Gen. Francis A. Walker in 1874, and the most extensive publication of this kind was published in 1893 as Weather Bureau Bulletin A, showing the frequency of storm-paths for all parts of the Northern Hemisphere. The wind, rain, and temperature are so distributed around a storm-centre that, when its location is known, the distribution of all the others can be closely estimated. In general, in the Northern Hemisphere, the regions that lie to the south of the paths of the storm-centres have prevailing warm, moist, southerly winds followed by occasional sudden changes to cool, dry, westerly winds. This change occurs with every passing storm-centre, but the prevailing weather is clear and pleasant. Stations lying on the north of the paths of the storm-centres have prevailing easterly winds, with cloud and rain followed by cool northwest winds; but the time occupied by the trying easterly winds is proportionately larger.
It is difficult to describe or exhibit the climatic peculiarities of any region without the use of charts. Elaborate publications of this kind, for United States weather, have issued from the Weather Bureau at Washington; the Climatic Charts for the Years 1870-99 show the normal precipitation for each quarter of the year, the normal percentage of sunshine, the normal barometric pressure, reduced to sea-level, the normal temperature of the air at the surface of the earth, the mean maximum and mean minimum temperatures, the highest and lowest recorded temperatures. In addition to these, charts of first and last frost and of prevailing winds have also been published. The ordinary popular textbooks on meteorology are very largely occupied with climatology, properly so called. Of these, that by Prof. Frank Waldo (New York, 1896) is probably the most complete for America; the treatises of Angot, Traité élémentaire de météor-
