What happened 1638 AD

In 1638, Galileo described an experimental method to measure the speed of light by arranging that two observers, each having lanterns equipped with shutters, observe each other's lanterns at some distance. The first observer opens the shutter of his lamp, and, the second, upon seeing the light, immediately opens the shutter of his own lantern. The time between the first observer's opening his shutter and seeing the light from the second observer's lamp indicates the time it takes light to travel back and forth between the two observers. Galileo reported that when he tried this at a distance of less than a mile, he was unable to determine whether or not the light appeared instantaneously.

The Emperor Go-Sai of Japan was born in 1638.

The First Lord of the British Admiralty, Henry Capell, was born in Hadham Parva, Hertfordshire.

The Schouwburg Theater is the first in Amsterdam.