Ever since photography was invented, men have been pressing it into service as a tool, dreaming of new ways to make it do what human eyes cannot: of speeding up time or slowing it down to learn how things actually behave; of making visible the things that are too small or too distant or too faint for the unaided eye to see; of utilizing other light waves that, like ultraviolet, are totally invisible to human beings, but are there just the same to register on the eyes of certain insects and on photographic emulsions.