The Window Pane

Refraction:
We have seen that light is bent when it passes from one medium to another of different density, and that objects viewed by refracted light do not appear in their proper positions.

When a ray of light passes through a piece of plane glass, such as a window pane, it is refracted at the point B toward the perpendicular, and continues its course through the glass in the new direction BC. On emerging from the glass, the light is refracted away from the perpendicular and takes the direction CD, which is clearly parallel to its original direction. Hence, when we view objects through the window, we see them slightly displaced in position, but otherwise unchanged. The deviation or displacement caused by glass as thin as window panes is too slight to be noticed, and we are not conscious that objects are out of position.

FIG. - Objects looked at through a window pane seem to be in their natural place.