Page:The American Cyclopædia (1879) Volume IV.djvu/691

CLIMATE 679 CLIMATE (Gr. /cAfyza, Fr. climat), the condi- tion of any portion of the earth's surface in respect to temperature, moisture, and other at- mospheric phenomena. The Greek original (from icMveiv, to slope or incline) was employed to signify the obliquity of the sphere, to which the inequality of the length of the day was due, the word primarily signifying an inclined plane or slope ; hence applied to a belt or zone of the earth's surface differing, for the reason above given, from another or contiguous belt in the length of its day. The geographer Ptolemy was the first to establish these belts and to de- fine them as climates ; dividing the surface from the equator to the 58th parallel into 25 such climates, differing a quarter of an hour each in the length of the longest day ; next from the 58th to the 63d parallel making four climates of one half hour's difference each, and from the 63d to the 66th parallel three climates of one hour each. From the polar circle to the pole there were six climates of one month's differ- ence each. At the equator the first belt was 4 15' in width, diminishing gradually till at the 45th parallel it was 1 50' in width, and at the 57th parallel 30' only. This irregular and fanciful division long remained, in consequence of the difficulty of attaining to any positive basis of distinction on astronomical or pure- ly geographical grounds. As discoveries ex- tended in all directions, and particularly to western Europe, distinctions founded on lati- tude or length of the day were found to be in- applicable and valueless, and they fell into dis- use long before observation began with the in- struments now in use to measure the heat, the weight of the air, &c. With the invention of these instruments the word climate came to signify the aggregate of atmospheric conditions affecting organic existence, animal and vegeta- ble ; and particularly the degree of heat, the winds, the rain, the changes in atmospheric weight, and all like sensible conditions. The barometer, developed from the Torricellian vacuum in 1 643, was the first instrument suit- ed to exact observation; soon afterward ex- pansible fluids were used as measures of heat, and good spirit thermometers were in use in 1680. But it was not till 1730 that mercury was substituted for spirit in part, and permanent series of observations began to be recorded ; the first in. America being at Charleston by the learn- ed Dr. Lining in 1738. Great activity existed near the close of the 17th century, when these instruments were novel, and when positive and even mathematical precision was hoped for through records of their observation ; and the earlier " Philosophical Transactions " of the royal society are full of papers and discussions on the subject. But it was soon found that there was no parallel in this to other depart- ments of physics, and interest in it greatly de- clined until the new and broad generalizations of Humboldt were put forth. To Sir William Herschel and Alexander von Humboldt the world is chiefly indebted for the rapid progress made in the science of climatology within the present century. Humboldt in 1817 published his celebrated treatise entitled Des lignes iso- thermes, et de la distribution de la cJialeur sur le globe, in which he showed that the de- crease of heat with the increase of latitude takes place more slowly on the west coasts of the old world than on the east of the new. He connected places having an average amount of temperature during the year by isothermal lines, the convex summits of which fell near the west coast of the old world, and their con- cave near the east coast of the new. By com- bining the decrease of temperature by increas- ing elevation with its decrease by increasing latitude, he represented the intersection of isothermal surfaces with a vertical plane cut- ting the surface of the earth along a meridian, and showed that if the examination of places of equal summer heat and equal winter cold were conducted in a similar manner by drawing iso- thermal and isochimal lines, the difference be- tween a sea and a continental climate would be included in the general view. These isother- mal lines differ materially from the parallels of latitude. It is not necessary to enter into detail as to how the annual rotation and oblique mo- tion of the earth in relation to the sun fix the tropical limits of the sun's apparent declination south and north of the equator, and produce alternate winter and summer on either side of the line, as it will be evident that the mean an- nual temperature obtained at different latitudes must decrease from the equator to the poles. Had the whole surface of the earth been uni- form, presenting the like relations to radiant heat, unaffected by the unequal action of dis- turbing causes, the mean temperature of every point would have been in proportion to the ra- dius of the parallel of latitude. But the mean temperature of places in the same lines of lati- tude differs very materially. .The isothermal line, for example, of 59 F. traverses latitude 42 in Europe, but descends to latitude 35 in America. Hence it appears that the mean an- nual temperature in the latitude of Beaufort, N". 0., 34 41', is nearly the same as that of Rome in latitude 41 54'; and it consequently follows that other causes are in operation in both of these different localities affecting the mean temperature than nearness to or remoteness from the equator. Accurate and long contin- ued observations are necessary to give value to meteorological facts. These have been pursued of late with much zeal. Kamtz and Mahlman have carefully represented annual isothermal lines, but Professor Dove was the first to re- duce these to monthly temperatures. The ob- servations of Professor Dove were first pub- lished in the " Transactions of the Royal Acad- emy of Sciences " in Berlin, in 1846, and have since appeared in the " Transactions of the British Association." These observations, which are of great value, and place their author among the first of living meteorologists, fully sustain the views of Humboldt, and natu-