Re: ex-meridian sights - further question
Subject: Re: ex-meridian sights - further question
From: Steven Wepster (wepster@XXX.XXX)
Date: Wed Feb 14 2001 - 09:12:46 EST
Most interesting. The Ex meridian method stems
from ancient times before the good Marc. Ste. Hilaire position line method.
However it appears
to be time honoured especially with DOT examiners. What has always
interested me is
why not simply use a sight taken 10 or so minutes
before or after noon ( up to 30 or so minutes
allowed by ex-merid tables) as a simple P/L. It
can be used with future or past P/L's to give a
position. Historically the idea of the ex-merid. was
that commercially it was most important to have
a noon position so that distance run and distance
to go was known and course fuel consumed,
slip and the rest of it calculated. Commercially of
course the noon pos. is still important although
usually worked from GPS. I dont want to knock
the users of the ex. merid. its just that I have never
had a use for it.
Regards
Barrie
Actually the ex-meridian latitude was invented by the Dutch teacher
Cornelis Douwes in the 1740s, ie before the steam-driven steel
vessels. The method was considered very useful because those were the
days before accurate chronometers were available for use at sea, there
was no notion of an altitude line of position, and Marc St Hilaire
wasn't even born yet. The ex-meridian method allows the navigator to
obtain a latitude fix on days when it is quite cloudy and the sun just
visible for a few seconds close to, but not at, local noon.
_Steven.
