Dust particles.
Hazes.
But desert air is not quite like the plateau air of Wyoming, though one can see through it for many leagues. It is not thickened by moisture particles, for its humidity is almost nothing; but the dust particles, carried upward by radiation and the winds, answer a similar purpose. They parry the sunshaft, break and color the light, increase the density of the envelope. Dust is always present in the desert air in some degree, and when it is at its maximum with the heat and winds of July, we see the air as a blue, yellow, or pink haze. This haze is not seen so well at noonday as at evening when the sun’s rays are streaming through canyons, or at dawn when it lies in the mountain shadows and reflects the blue sky. Nor does it muffle or obscure so much as the moisture-laden mists of Holland, but it thickens the air perceptibly and decreases in measure the intensity of the light.
Seeing the desert air.
Sea breezes on desert.
Yet despite the fact that desert air is dust-laden and must be thickened somewhat, there is something almost inexplicable about it. It seems so thin, so rarefied; and it is so scentless—I had almost said breathless—that it is like no air at all. You breathe it without feeling it, you look through it without being conscious of its presence. Yet here comes in the contradiction. Desert air is very easily recognized by the eyes alone. The traveller in California when he wakes in the morning and glances out of the car-window at the air in the mountain canyons, knows instantly on which side of the Tehachepi Range the train is moving. He knows he is crossing the Mojave. The lilac-blue veiling that hangs about those mountains is as recognizable as the sea air of the Massachusetts shore. And, strange enough, the sea breezes that blow across the deserts all down the Pacific coast have no appreciable effect upon this air. The peninsula of Lower California is practically surrounded by water, but through its entire length and down the shores of Sonora to Mazatlan, there is nothing but that clear, dry air.
Colored air.
Different hues.
I use the word “clear” because one can see so far through this atmosphere, and yet it is not clear or we should not see it so plainly. There is the contradiction again. Is it perhaps the coloring of it that makes it so apparent? Probably. Even the clearest atmosphere has some coloring about it. Usually it is an indefinable blue. Air-blue means the most delicate of all colors—something not of surface depth but of transparency, builded up by superimposed strata of air many miles perhaps in thickness. This air-blue is seen at its best in the gorges of the Alps, and in the mountain distances of Scotland; but it is not so apparent on the desert. The coloring of the atmosphere on the Colorado and the Mojave is oftener pink, yellow, lilac, rose-color, sometimes fire-red. And to understand that we must take up the ground-glass globe again.
Producing color.