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Hello, my name is Robert van Gent and I am a new member to this list. I
am interested in the history of astronomy and its application in related
fields such as calendars and navigation.

I joined this list in the hope that questions relating to the history of
navigational sciences and techniques would also be discussed on this
platform, but if I am seriously mistaken, I would be grateful if someone
on this list could set me on the correct path (or should I say course?).

I have two questions which I hope someone on this list can help me with.

1) I am trying to locate an obscure reference cited in Bowditch�s
_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 the application of the standard
formula for the correction for dip:

  dip (minutes of arc) = 0.97 sqrt(h[ft])

with 'h' denoting the height of the observer�s eye above sea level in
feet.

The constant 0.97 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 to this study.

2) My second question is of a more cartographical nature. After
inspecting several 20th-century atlases I noticed that in each source
the International Date Line (IDL) is drawn along a slightly path and
that no two atlases agree completely. Is there such a thing as an
Internationally agreed Date Line? If so, who decides on these matters?
And what do countries who straddle the IDL have to say in this matter?

As everyone probably already knows the issue has become more complicated
since 1995 when the island Republic of Kiribati decided to shift the
IDL, which bisected the country, to follow its eastern boundaries. Which
leads to another question again: what are the internationally recognized
borders of Kiribati? Again different recent atlases represent them
slightly differently.

I measured a set of approximate co-ordinates for the corner points
defining the eastern boundary of Kiribati from the _National Geographic
Atlas of the World_ (6th ed., 1992). Rounded to the nearest degree, I
found the following latitudes and longitudes (positive in eastern
direction):

  {+2,180},
  {0,-179},
  {0,-165},
  {-3,-165},
  {-3,-160},
  {+2,-160},
  {+2,-162},
  {+5,-162},
  {+5,-154},
  {-8,-151},
  {-12,-151},
  {-12,-157},
  {-9,-157},
  {-9,-178}

Does anyone on this list know how to obtain more accurate figures?

Happy sailing to all.

================================================================
* Robert H. van Gent * Tel/Fax:  00-31-30-2720269              *
* Zaagmolenkade 50   * E-mail:   r.h.vangent@astro.uu.nl       *
* 3515 AE Utrecht    * Home page (under construction):         *
* The Netherlands    *           http://www.fys.ruu.nl/~vgent/ *
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