THE Victorian writer and critic, John Ruskin, liked to extol nature's artistic creativity at length. "While it is true that the dusky atmosphere obscures all objects," he wrote, "it is also true that nature never intended the eye of man to be without delight, and has provided a rich compensation for shading the tints with darkness, in their brightening by moisture. Every colour, wet, is twice as brilliant as it is when dry and when distances are obscured by mist, and bright colours vanish from the sky, the grass and foliage revive into their perfect green.
Now some might feel that Ruskin exaggerates the visual pleasures of a dismal day. The kernel of his argument, however, is that "every colour, wet, is twice as brilliant as it is when dry", and in that he absolutely right. It is interesting to speculate why this is so.
Most objects appear to be a certain colour because their molecular structure is such as to absorb certain wavelengths of light and to reflect others. In the case of grass, for example, all colours except those which make up the colour green are absorbed the unabsorbed green light is "rejected" and registers as that colour when it hits our eyes.
When sunlight hits a blade of grass, however, some of the incident light is "scattered" in all directions by tiny irregularities on its surface before the process of selective absorption can take place. Some of this scattered white sunlight will be redirected towards an observer, wherever he or she may be, and has the effect of overlaying the green colour of the grass with a whitish tinge the green, in a sense, appears lighter than it really ought to be. But when the grass is wet, its surface is covered with a thin film of water, and being smoother than it was before, it no longer scatters the incident white light to the same extent for this reason, its intrinsic green colour predominates and appears much more vivid than it was before the wetting.
A similar process can be seen at work when the first drops of rain on a sandy surface stand out as very dark spots. Because the newly arrived water penetrates every little space between the grains, rays of light which otherwise might have been scattered towards an observer by the topmost layers now penetrate more deeply into the dust before being sent back in his or her direction. Much of the light is absorbed on its adventures along this longer path, less therefore returns in the direction of our eyes, and so each little wet circle appears much darker than its dry surroundings.