American Scientist

Until just a few generations ago, shadows were always moving. No shadow was ever really still. Candles and hearths project shaky, agitated shadows on the walls of a room. Outdoors, all you have to do is trace an outline and then come back to it a few minutes later to see the movement of apparently static shadows cast by bodies in sunlight. Sundials work because of the movement of shadows. Artists have always had great difficulty painting landscapes or buildings lit by the sun. After an hour passes, the distribution of shadows in the landscape has changed so much that the view is unrecognizable. Partly for this reason, painting classes study the theory of shadows, which frees objects from the constant mutation of natural chiaroscuro.

The pioneers of photography faced a similar problem. The photographic technique invented by Joseph-Nicéphore Niepce (1765– 1833) uses a bituminous substance that becomes insoluble when exposed to light. Unfortunately, eight hours of exposure is required, and in that time shadows move quite far around the subjects. If you want to freeze a shadow, you can make do with shadowgraphs, as did William Henry Fox Talbot (1800–1877): you immerse paper in sea salt and then in a silver nitrate solution, you artistically lay leaves, cutouts, and lace directly onto the surface, and you allow the sun to darken the bare parts while leaving the covered parts white. But then the only objects that you can capture in the image are just as flat and devoid of nuance as the shadows that represent them.

Modern shadows—stuck to walls, jammed between houses—are like a new species that has populated the earth by colonizing the empire of the night. . . .

The Shadow Club: The Greatest Mystery in the Universe—Shadows—and the Thinkers Who Unlocked Their Secrets
Roberto Casati
Alfred A. Knopf, $24