Dead Reckoning, with the 'a'

On Wed, 11 Aug 2004 06:53:09 -0400, Cub Driver
wrote:

On Tue, 10 Aug 2004 12:35:57 GMT, "Daniel L. Lieberman"
wrote:

The log is the ships log - not a log in the water.

Actually not. The log referred to was the object (originally rather
like a log) thrown over the stern. It was attached to a string which
had knots in it, and however many knots passed through the navigator's
fingers in a given period of time measured the ship's speed.

Thus log -- and thus knots.

It enabled dead reckoning because it enabled the navigator to know the
ship's speed more or less accurately.

Exactly--I think you've hit the nail on the head. More details
from http://dictionary.reference.com/search?q=log%20board
show how the name of the book got derived from the log thrown
overboard to calculate a ship's speed. I imagine that our "logging
in" and "logging out" of computer systems is derived in turn from
the ship's log book.

2. [Prob. the same word as in sense 1; cf. LG. log, lock, Dan. log,
Sw. logg.] (Naut.) An apparatus for measuring the rate of a ship's
motion through the water.

Note: The common log consists of the log-chip, or logship, often
exclusively called the log, and the log line, the former being
commonly a thin wooden quadrant of five or six inches radius, loaded
with lead on the arc to make it float with the point up. It is
attached to the log line by cords from each corner. This line is
divided into equal spaces, called knots, each bearing the same
proportion to a mile that half a minute does to an hour. The line is
wound on a reel which is so held as to let it run off freely. When the
log is thrown, the log-chip is kept by the water from being drawn
forward, and the speed of the ship is shown by the number of knots run
out in half a minute. There are improved logs, consisting of a piece
of mechanism which, being towed astern, shows the distance actually
gone through by the ship, by means of the revolutions of a fly, which
are registered on a dial plate.

3. Hence: The record of the rate of ship's speed or of her daily
progress; also, the full nautical record of a ship's cruise or voyage;
a log slate; a log book.

4. A record and tabulated statement of the work done by an engine, as
of a steamship, of the coal consumed, and of other items relating to
the performance of machinery during a given time.
....
Log board (Naut.), a board consisting of two parts shutting together
like a book, with columns in which are entered the direction of the
wind, course of the ship, etc., during each hour of the day and night.
These entries are transferred to the log book. A folding slate is now
used instead.

Log book, or Logbook (Naut.), a book in which is entered the daily
progress of a ship at sea, as indicated by the log, with notes on the
weather and incidents of the voyage; the contents of the log board.

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19th century log-chip:
http://www.nmsi.ac.uk/piclib/imagerecord.asp?id=10284362

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Marty