[Arjen Markus] (4 may 2006) It occurred to me that we do not yet have a decent module in Tcllib yet that collects the 
various physical empirical formulae. So, right now, if I want to compute the water content of air, I have to hunt 
the Internet for the right formula. Similarly, the density of water as a function of temperature and salinity.

I am probably not the only one with that little problem, so I propose to collect such formulae here (with a
reference) so that later we can simply wrap them up in a package/module for Tcllib.

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A formula for the humidity content of air:

   set vapordens [expr {5.018+0.32321*$td+8.1847e-3*$td*$td+3.1243e-4*$td*$td*$td}]

Symbols:
   * td the dewpoint temperature in degrees C
   * vapordens the water vapour density in g water/m3 

Reference:
http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/relhum.html#c2
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[Category Physics]
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