Re: World's first computer may be even older than thought

On Wed, 29 Jul 2009 15:34:40 -0700 (PDT), Jack Linthicum
<jacklinthicum@xxxxxxxxxxxxx> wrote:

That never sail out of sight of land is a total myth, especially by
the 2nd C BC when this thing is supposedly built. Making noon sun line
observations with a known ideal for comparison would be useful in
doing the long distance haul. Also, I'm not sure how it was supposed
to work but one of the rivals for finding longitude in the 18th C was
"lunars". Again with a known standard, which we put in print until the
satellite stuff came into play, provides a check.

Imagine a cargo ship sailing just in daylight, putting ashore every
night, which would require unloading, setting up camp, cooking a
meal,sleeping, getting up, cooking a meal, reloading the ship and
setting sail.

Mathematical astronomy and shipboard instruments did not get good
enough to use lunar distances until the 18th century. To figure your
longitude to one degree you need to know the position of the Moon to
better than 2 minutes of arc. Newton developed in 1702 a lunar theory
that was the first to give predicted lunar positions with the needed
accuracy. Hadley demonstrated his sextant in 1732. Those were the
ingredients you needed for lunar distances. Prior to that you
determined longitude at sea by dead reckoning. Ancient sailors did
the same. Experienced seamen who knew their trade routes would know
and use all sorts of details of currents and so on for navigation. I
expect that they wouldn't lay up unless the weather was unfavorable.

A Google search turned up a book, "Homeric Seafaring" by Samuel Mark,
that looks interesting, if expensive (sixty bucks).

Bud
.

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