At the same time color came in. We are not accustomed to realize that nature drew the Earth in grays and greens, and touched it up with color afterward. Only the tempered tints of the rocks and the leaden blue of the sea, subdued by the disheartening welkin overhead to a dull drab, enlivened their abode for the oldest inhabitants. But with Tertiary times entered the brilliantly petalled flowers. Beginning with yellow, these rose through a chromatic scale of beauty from white through red to blue.[24] They decked themselves thus gaudily because the Sun was there to see by, as well as eyes to see. For without the Sun those unconscious horticulturists, the insects, could not have exercised their pictorial profession. [23] Dana, Geikie, De Lapparent. [24] Cf. Grant Allen. To the entering of the Sun upon the scene this wondrous revolution was due; and once entered, it became the dominant factor in the Earth’s organic life. We are in the habit of apostrophizing the Sun as the source of all terrestrial existence. It is true enough to-day, and has been so since man entered on the scene. But it was not always thus. There was a time when the Sun played no part in the world’s affairs. As its heat is now all-important, it becomes an interesting matter to determine the laws governing its amount. That summer is hotter than winter we all know from experience, pleasurable or painful as the case may be. This is due to the fact that the Sun is above the horizon for a greater number of hours in summer and passes more directly overhead. But not so many people are aware that on midsummer day, so far as the Sun is concerned, the north pole should be the hottest place on earth. That Arctic explorers, who have got within speaking acquaintance of it, assure us it is not so, shows that something besides the direct rays of the Sun is involved. Indeed, we learn as much from the extensively advertised thermometers of winter resorts which, judiciously placed, beguile the stranger to sojourn where it is just too cold for comfort. The factor in question is the blanketing character of our air. Now a blanket may keep heat out as well as keep it in. Our air acts in both capacities. It is by no means simply a storer of heat, as many people seem to suppose; it is a heat-stopper as well. What it really is is a temporizer, a buffer to ease the shocks of sudden change like those comfortable, phlegmatic souls who reduce all emotion to a level. For the heating power of the Sun, even at the Earth’s distance away, is much greater than appears. Knowledge of this we owe most to Langley, and then to Very, who continued his results to yet a finer determination, the best we have to-day. In consequence we have learnt that the amount of heat we should receive from the Sun, could we get above our air,—the solar constant, as it is called,—would be over three times what it is on the average in our latitude at the surface, and is rising still, so to speak.