Sir Benjamin Thompson (AKA Count Rumford) (March 26, 1753 – August 21, 1814)
Rumford was a pioneer of photometry, the measurement of light. He invented a photometer and introduced the standard candle, the predecessor of the candela, as a unit of luminous intensity. His standard candle was made from the oil of a sperm whale, to rigid specifications.
Thompson was given the task of removing all the beggars from the streets by the Munich government. In return he became Count Rumford.
His experiments with light were primarily aimed at finding the cheapest method of lighting the workhouses in which the beggars were going to be imprisoned.
He used coloured filters to reduce the intensity of the light from both sunlight and lamps. While doing so he noticed an unusual result -- placing a red filter over a light source would give rise cyan shadows. If he isolated the shadow by viewing it through a small tube, the shadow would appear neutral in colour.
The cyan shadow was a product of our brain, it did not exist in reality.