In a submarine beneath the ocean’s surface, a captain peered into a long tube to see possible threats in the sea and air above. This sight tube, called a periscope, was designed by the Frenchman Marie Davey in 1854. Davey’s periscope contained two mirrors, one placed at each end of a vertical tube. The mirrors were set parallel to each other and at 45 degrees to the vertical. The reflective surfaces faced each other. When light from an object on the surface reflected downward, an image appeared to the eye. People in submerged submarines could see what was above them! Imagine you are in a submerged submarine looking through a periscope. What are some things you might see?