…of their causes, because the darkness composed of the thickness of the clouds, besides the privation of the solar rays, tints with itself whatever it touches. But the surrounding air outside the clouds and shadows sees and illuminates the same place, and makes it partake of the blue color; and the air penetrated by the solar rays, which is found between the darkness of the aforesaid shadow of the earth and the eye of the beholder, also tints that place with the blue color, as it is proved that the blue of the air is born of light and of darkness. But the part of the landscape illuminated by the sun partakes of the color of the air and of the sun, yet partakes much of the air, because it acts as the greater, the air being nearer, and it becomes a field of innumerable suns as regards the eye. And these landscapes will partake the more of blue the more remote they are from the eye; and that blue will become the paler the more it rises toward the horizon, and this comes from the humid vapors.

Things are less noticeable in the shadows than in the lights, and the universal light surrounds the shadowed bodies and leaves them with little relief. When the eye interposes itself between the shadowed body and the light, the shadow is invisible to that eye; but the lateral bodies at such a time will show their lights in greater or lesser quantity, according as those bodies are nearer or more remote from the straight line that extends from one horizon to the other, passing through the two seeing eyes of that landscape.