This sub-directory contains extinction law (".ext") files, which
describe extinction curves.
- In each file there is one line per data-point. The first column
  is the wavelength, in Angstroems. The second column contains the
  extinction in relative optical depth.
- Comment lines must begin with `#'.
- Wavelengths must be sorted by increasing lambda.
- optical depths are linearly interpolated between data-points
  by SkyStuff.
- Each extinction law must explicitely begin and end
  with optical depth equal to 0.

				Emmanuel BERTIN <bertin@iap.fr>
