I am trying to locate an obscure reference cited in Bowditchs _American Practical Navigator: An Epitome of Navigation_ (p. 423, 1958 edition; vol. II, p. 546, 1977/81 edition) to a study performed by the Carnegie Institute of Washington on refraction in the terrestrial atmosphere.
As is well known the terrestrial atmosphere affects the paths of light rays near the horizon, causing the observed horizon to be slightly lower than the geometrical horizon. The small angle between both horizons is known as the 'dip', and can be approximated by the following relation found in almost any astronomical or navigational handbook: dip (minutes of arc) = 0.97 sqrt(h[ft]) with 'h' denoting the height of the observers eye above sea level in feet. The constant in the above relation depends on the local atmospheric conditions and the quoted value applies to average weather conditions. The studies by the Carnegie Institute appear to have been made to verify how well this relation stands up to varying weather conditions and how large the deviations can be in extreme cases. I would be most grateful if someone on this list can provide me with a more complete reference. ================================================================ * Robert H. van Gent * Tel/Fax: 00-31-30-2720269 * * Zaagmolenkade 50 * E-mail: [EMAIL PROTECTED] * * 3515 AE Utrecht * Home page (under construction): * * The Netherlands * http://www.fys.ruu.nl/~vgent/ * ================================================================