Fiber Aquatics, by Henry Mecredy, Houston
The technology of fiber optics is based on the principle that light striking a surface at a shallow-enough angle will reflect off of the surface instead of penetrating through it. (The discovery of this principle is usually attributed to Snell.) The surface in question can be simply any interface between two light-transmitting substances, such as glass and air, or water and air, or glass and water. An optical fiber is just a glass strand in which light introduced at one end undergoes "total internal reflection" along the walls, and emerges at the other end.
It's easy to observe this phenomenon by descending gently into a calm swimming pool, then looking back upward at the surface of the water. If you look straight up or nearly so, you will simply see the outside, air-infested, humdrum world to which you are accustomed. There will be the clouds, or the lifeguard stand, or the roof of the pool. However, if you lower your gaze and look at the surface at a low angle -- as though trying to see the horizon-- you will instead see the reflections of things under the water, such as the lane stripes, or the pool drain, or -- if you are lying horizontal on your back, as during a pushoff from a backstroke turn -- your legs and feet.
Usually, the pool surface is all chopped up, so looking at the surface from the real world back toward the Air World, you see a totally incomprehensible image composed of little imagelets; bent, wrinkled, magnified; reflected and transmitted from all over the place, above and below the water.
In the summer, I swim at sundown in a 50-meter pool located on a prairie, part of the Texas coastal plain. The sunsets are often really beautiful, with the sun taking on a rich, reddish-golden color which the underlit clouds amplify. Because the pool is shallow and unshaded, there is an aerator cooling system which shoots hundreds of streams of water out over the pool in a series of arcs, forming a sort of tunnel along one side of the pool. Sometimes warming up in an otherwise empty pool I swim under this tunnel, such that on alternate lengths, when I turn my head to breathe, I am looking west toward the sunset, and toward the place where all these streams of water are descending onto the pool surface.
Normally, since I am looking obliquely at the bottom of the air-water interface, I would see the black-striped, turquoise reflection of the distant, already-shadowed lanes of the pool. But the surface a few feet in front of my face is spattered with drops from the aerator, making thousands of little divots. Each divot briefly distorts the plane of the surface and permits a little chunk of transmitted light--magically containing a bright piece of sunset color -- to flash into the midst of the subdued, reflected turquoise background. All in all, it's a jewel-like display that shows once more that fitness is not the only reason to swim.
(by Henry Mecredy published in Gulf Masters Newsletter, January, 1997)
