Page:Popular Science Monthly Volume 54.djvu/245

Rh upon them. The rhythm of the world has set up an organic rhythm which now spontaneously and automatically follows it.

At first sight, to the dweller in the temperate zone at the present day, the questions I have put above may seem needless, not to say childish. But that is perhaps because we have all too much the habit of taking it for granted that what is true here and now has also been true everywhere and always. A first visit to the tropics often enough rudely disturbs this uninquiring attitude of mind. For in the tropics, and especially in the equatorial region, there is no winter and no summer, no spring and no autumn. The world wags wearily through an unending display of monotonous greenery. As far as temperature goes, the year is pretty much alike in all its months. Yet not only do equatorial men recognize the existence of the year as a natural epoch quite as much as other men—not only do equatorial savages celebrate annual feasts, count ages by years, and perform certain rites in certain months only—but also animal and vegetable nature recognizes the year; trees have their month for blossoming and fruiting, birds their month for assuming the plumage of courtship, for nesting and hatching, almost as markedly as elsewhere. The recognition of the year both by man and by Nature is not therefore entirely dependent upon the difference of summer and winter, as such. We must go deeper, and I think, when we come to consider geological time, much deeper, if we wish to understand the true character of yearliness—a word which I venture here to coin to express this meaning.

Have you ever quite realized what the tropical year is like? Suppose you are living on or near the equator, then in December the sun is south of you and at its greatest distance away; you have, so to speak, a relative winter. But in March the sun is overhead; it is now full midsummer. By the end of June the sun has gone north, and is once more on a tropic; you have a second winter; not much of a winter, I admit, but still, a relative winter. By September he has returned overhead again, and you are enduring a second summer. In December he has once more retreated to the southern tropic (Capricorn), and it is comparative winter. Thus the equatorial year consists of four distinct seasons, in two of which the sun stands directly overhead, while in two he is at his northern or southern limit. I may add that the effect is always curious when, as you face the sun, you see that he is moving in his diurnal path, not from left to right ("the way of the sun," as we say), but from right to left (or "widdershins"). You are never till then aware how natural and inevitable has seemed the opposite direction: when you find it reversed the effect is surprising.

Now, the distance to which the sun travels north or south of you,