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THE AMERICAN JOURNAL OF SOCIOLOGY
For the former, the averages for winter and summer vary little ; for the latter, the divergence increases ; the same latitude does not necessarily have the same climate. If, by a continuous line, we unite, on the globe, localities having the same average winter temperature, and by another line those having the same average summer temperature, we obtain two lines, the one isocheimal, the other isotheral, the curves and irregularities of which follow the unequal distribution of seas and continents. The isothermal line is that which results from the general average of the temperature for the year. Within the tropics the lines of lati- tude and the isothermal lines tend to coincide.
The maximum line of temperature cuts the terrestrial equator under the meridian of Singapore and Tahiti, traverses the southern portion of the Pacific Ocean, and the northern part of the Atlantic. The average temperature corresponding to this thermal equator is 28?8o'
In addition to the two fundamental, external and internal, causes indicated above, the average temperature depends, also, upon such particular causes as height above the sea-level, the hygrometrical condition, winds, some of which are more constant than others, and certain ocean currents, such as the Gulf Stream. The opening of the Isthmus of Panama, if it should modify the direction of this warm current, could influence the temperature of certain parts of Europe.
The earlier historians, philosophers, and political theorizers have generally accorded an excessive and too invariable influence to climate, not only on the distribution of the different varieties of the human species, but on their physical, moral, and intel- lectual qualities, and on the form of their governments. This influence is far from being unique and absolute ; it is only rela- tively constant. The results of a more thorough observation of diverse civilizations in different times and places have reduced the influence of climate to more feeble variations. However, from the time of Herodotus and Aristotle to that of Montesquieu, it seems to have been given the dominant place, and such is still given it even in the eyes of some of the creators of the contemporary philosophy of history.
