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Re: downy dinos

At 11:23 PM -0600 9/1/01, Richard W Travsky wrote:
On Sat, 1 Sep 2001, Jeff Hecht wrote: 
 At 3:20 PM -0700 9/1/01, Waylon Rowley wrote:
 > [...]

 That doesn't work for polar bears, and I don't see how it would work
 for feathers. Light guiding is a complex process; it would require
 feathers designed not for flight but for light guiding, and nothing
 today does that. (Merging the inputs from different filaments on the
 feather would be quite complex.)


Maybe not as complex as we thought. Recently two different sea creatures
have been shown to have light guiding structures.

Rossella racovitzae, an antarctic sponge, has glassy spines (described in
the August 4th Science News as being a "finger length or two" in length)
that gather light.

There are a number of biological examples of light guiding, generally over quite short distances. One example lies within the rods and cones in the retina, which guide light along their length to the light-sensing regions at the backs of the cells. My point was that polar bear hair is not fiber-optic, and that the mechanism of collecting exterior light to "pipe" through a hair or feather to the skin is unrealistic. In addition, true 'fiber-optic' light guiding requires a core of higher refractive index than the surrounding material -- not a hollow core. It is possible to guide some light through a hollow core (which has a lower refractive index than the surrounding material), but it's not as efficient as guiding light through a fiber.

The sponge spicules are glass with a uniform refractive index surrounded by sea water, which has a lower refractive index, creating an optical fiber effect. They are not hollow (like polar bear hair). Hollow structures in feathers, like polar bear hair, wouldn't work well.

-- Jeff Hecht