Heap clouds at sunset.
All the other cloud-forms, being more or less transparent, seem to aid rather than to obscure the splendor of the sky. The most common clouds of all are the cumuli. In hot summer afternoons they gather and heap up in huge masses with turrets and domes of light that reach at times forty thousand feet above the earth. At sunset they begin to show color before any of the other clouds. If seen against the sun their edges at first gleam silver-white and then change to gold; if along the horizon to the north or south, or lying back in the eastern sky, they show dazzling white like a snowy Alp. As the sun disappears below the line they begin to warm in color, turning yellow, pink, and rose. Finally they darken into lilac and purple, then sink and disappear entirely. The smaller forms of cumulus that appear in the west at evening are always splashes of sunset color, sometimes being shot through with yellow or scarlet. They ultimately appear floating against the night sky as spots of purple and gray.
Strati.
Above the cumuli and often flung across them like bands of gauze, are the strati—clouds of the middle air region. This veil or sheet-cloud might be called a twilight cloud, giving out as it does its greatest splendor after the sun has disappeared below the verge. It then takes all colors and with singular vividness. At times it will overspread the whole west as a sheet of brilliant magenta, but more frequently it blares with scarlet, carmine, crimson, flushing up and then fading out, shifting from one color to another; and finally dying out in a beautiful ashes of roses. When these clouds and all their variations have faded into lilac and deep purples, there are still bright spots of color in the upper sky where the cirri are receiving the last rays of the sun.
Cirri.
Ice-clouds.
The cirrus with its many feathery and fleecy forms is the thinnest, the highest, and the most brilliant in light of all the clouds. Perhaps its brilliancy is due to its being an ice-cloud. It seems odd that here in the desert with so much heat rising and tempering the upper air there should be clouds of ice but a few miles above it. The cirrus and also the higher forms of the cumulo-stratus are masses of hoar-frost, spicules of ice floating in the air, instead of tiny globules of vapor.
Clouds of fire.
The celestial tapestry.
There is nothing remarkable about the desert clouds—that is nothing very different from the clouds of other countries—except in light, color, and background. They appear incomparably more brilliant and fiery here than elsewhere on the globe. The colors, like everything else on the desert, are intense in their power, fierce in their glare. They vibrate, they scintillate, they penetrate and tinge everything with their hue. And then, as though heaping splendor upon splendor, what a wonderful background they are woven upon! Great bands of orange, green, and blue that all the melted and fused gems in the world could not match for translucent beauty. Taken as a whole, as a celestial tapestry, as a curtain of flame drawn between night and day, and what land or sky can rival it!