Sumner lines
Subject: Sumner lines
From: nigel_gardner (Nigel_Gardner@XXX.XXX)
Date: Sun Feb 18 2001 - 05:40:55 EST
The 'Sumner Line' was described by Captain Sumner in a book he published in
1843 in Boston. Bound from Charleston to Greenock in the South-west
approaches (South of Ireland) on 17 Dec 1837, not having had a sight for
some time and thus unsure of his latitude, he got a sight about 10am,
worked out the longitude from the sight for three different latitudes. He
noticed that the three different points lay in a straight line which ran
through the Smalls Light. He concluded "that the observed altitude must
have happened at all three points, at the Smalls light and at the ship at
the same instant of time". His method (calculating the longitude for two
different latitudes and running aposition line through them) was in use
certainly into the beginning of the 20thC although by that time Lecky and
others were advocating calculating one longitude from a DR latitude and
drawing line at right angles to the sun's calculated azimuth.
It might be well to remember the ethos of the age, as a previous
contributor has commented, one has to get into the mind of the 18/19C
mariner, "getting a fix" was not the be-all and end-all of things. A
longitude by the Prime Vertical at breakfast and latitude by mer-pass at
lunchtime served most of their needs.
NG
