A photographic demonstration of refraction; or the slowing of light. Many people do not understand that the speed of light is only a constant in a vacuum, but really as light passes through any transparent substance it slows.
Every transparent substance whether air, water, glass, or sapphire has a refractory index, or the amount that light slows as it passes through. You can demonstrate this simple concept to your children next time you are by the waterside on a sunny day by poking a stick into the water.
Like the image above, the part of the stick below the surface will appear shifted, or bent away from the part above the water. That’s because the light reflected from the portion beneath the surface travels back to your eye slower as it passes through the water, while the light reflected from the above-surface segment of stick travels faster as it passes through air. So slowing of light bends its path.
Light refraction (as well as other spectrum refraction) is an interesting property of physics with some potential. In the 80’s the University of Chicago created a sapphire solar furnace on their roof that reached temperatures hotter than the surface of the sun. (The sun’s surface, while hot, is somewhat cooler than the corona or the reactions taking place in the interior.)
This article at Wikipedia has more, please note that it references refraction as “bending of light”, however the bend is really the effect and result of the speed change. Also of interest is the link embedded in the article regarding negative refractory index materials, or “metamaterials“. Soon we might have true “cloaking devices”.
