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An additional comment regarding the sunset observations made by
Schaefer and Liller:

Unfortunately they don't mention in their paper the meteorological
conditions (temperature, pressure) at the time of the observations.
The variations of the published refraction values contain therefore
also the variations in meteorological conditions.

For those of you who have an interest in these observations:
I tried to retrieve this missing information from balloon soundings
which have been made in those days at Qunitero. (In the mean time this
sounding site has been abandoned.) This place is near the coast about
20 km north of Vina del Mar and about 250 km south of Cerro Tololo.
The sounding station has the codes 85543 and SCER. The data can be
obtained e.g. from this Web-page
http://weather.uwyo.edu/upperair/sounding.html The sunset observations
were made at around 22h/23h UTC; this is close to the 00Z soundings of
the following day. The temperature and pressure values have been
obtained by interpolation between the nearest sounding data. The
height information in the sounding data are geopotential heights; they
differ slightly from geometrical heights. For Vina del Mar this
difference is negligible; for Cerro Tololo the geometrical height of
2215m was found to correspond to 2240m geopotential height. A few
sounding data are missing; in those cases the values were obtained by
further interpolation between the nearest available ones. The results
have been compiled in the attached two Excel sheets. The values for
Vina del Mar should again be verified since I don't remember if the
interpolation were made for the correct height.

Marcel

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