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Re: _Sinosauropteryx_ fibers

Ralph Miller said:
>To offer a simplistic analogy: would a glass tube such as a laboratory
>pipette, for example (although admittedly geometrically dissimilar to the
>fur fiber at the distal end), be capable of conveying light or heat from
>one end to the other in spite of its hollow aspect?  Perhaps you could
>picture a polar bear fur fiber as a long, hollow acrylic cone for the sake
>of comparison, then stretch the length of the cone further in your mind's
>eye until it is a clear, hollow fiber which would still perform optically
>as the original cone model in certain respects.  Would this shape be
>capable of transmitting radiant energy?  I am asking; fiber optics are not
>my specialty.

Well, I've written a _lot_ about fiber optics, so I probably ought to say a
couple of things.

First, while polar bear fur is relatively clear at visible wavelengths, the
idea that the hairs function as light guides to warm the animal is a
scientific "urban myth." For more details, see the letter by D. M. Lavigne,
on p. 8 of the Sepbember 1988 SCIENTIFIC AMERICAN. His major points are
that polar bear fur is black in the ultraviolet, and traps the ultraviolet
light, helping raise the animal's skin temperature.

Second, a hollow transparent tube can guide light more weakly than an
optical fiber by a different effect. The fraction of light reflected by a
surface increases with the steepness of the angle it hits the surface at.
That is, the smaller the angle between the light rays and the surface, the
higher the reflectivity. This effect works for materials with refractive
index higher than air; you can find the equations in a good college optics
text. It would guide light along hollow fibers, but not as efficiently as
total internal reflection guides light through clear glass. (Total internal
reflection works for light trapped in a medium with higher refractive index
than the surrounding material -- i.e., a bare glass fiber in air, or a
fiber with a high-index core surrounded by a low-index cladding.

-- Jeff Hecht