189 We use the expression “external nature” through the whole of this work in contradistinction not only to the soul, but also to man’s body, designating his entire physico-intellectual activity by the term “labor-force” (_Arbeits kraft_). 190 By the expression “natural forces,” we designate the economically useful changes of matter, changes of place as well as of composition, which are made without man’s cooperation; for instance, the gigantic machinery which supplies the greater part of mankind with water to drink, for domestic and other purposes—the evaporation of the sea, the formation of clouds, rain, springs, rivers etc. See _Bastiat_, Harmonies, 277. Thus the sun’s rays are indirectly the cause, not only of vegetation, but also of all wind and steam forces. 191 Spite of this “freedom,” it may well happen that these gifts of nature can be utilized, in many cases, only on condition of some expenditure. The photographer can compel the sunlight to work for him only by means of a camera obscura, and the smithy the atmosphere, only by means of a bellows. But neither will ever successfully make an item, in their accounts with their customers, of the services of the sun or air. 192 The most important ocean currents may be explained by two causes: the flowing of the water from the polar seas to the equator (polar current), and the revolution of the earth about its axis (equinoctial current); besides which, there are the reflex currents produced by the horizontal form of the coast-lands. Thanks to these natural ocean highways, England is nearer to almost all the important mercantile coasts of the world by 300 geographical miles than the Eastern States of the American Union. The only exception is the Atlantic coast of America north of the Equator. North Americans to pass the line, or to double one of the two great capes, are obliged first to traverse the ocean as far as the Azores. On the other hand, the western coast of South America is very widely separated from Mexico, for instance, by its ocean currents. The colonization of America by Europe, instead of by China, is a consequence of the direction of ocean currents, as is also the fact that America has now the fairest prospect of influencing the civilization of China and Japan. What an influence the warm gulf stream has on the mild climate of north-western Europe! 193 While the Mississippi has no ebb or flow whatever, the influence of the ocean is felt in the Hudson, which is 60 geographical miles long, a distance of 29 miles from its mouth.