Text 23563, 79 rader
Skriven 2008-11-09 19:54:11 av Roy Witt (1:397/22)
  Kommentar till text 23532 av Dan Ceppa (1:138/666.0)
Ärende: Facts & Belief
======================
09 Nov 08 13:03, Dan Ceppa wrote to Roy Witt:

 DC>> That only gives him lattitude,  Longitude requires knowing
 DC>> accurately the time difference from the prime meridian.  Without
 DC>> that, east west distance is pure guess work.

 RW>> Who was it that you mentioned accurately measured the diameter of
 RW>> the earth, some thousands of years before Columbus attempted this
 RW>> voyage?

 DC> I thought it was you!  It must have been in a message to you.

I have to admit that I went back a few pages and took the name from your
message and used it in my message. I even made the effort to look it up on
Wiki, to make sure it was correct. But, the name escapes me now.

 RW>> Had Columbus used those figures, he could have very accurately
 RW>> determined his postion by the above method with the aid of an Hour
 RW>> Glass to determine his lattitude. Since they also knew that there
 RW>> were

 DC> Latitude is easy to find.

 RW>> certain stars in some constellations and their positions, they could
 RW>> have also determined their longitude. I know that's hindsight, but
 RW>> if they had picked someone smarter to make the journey, it may have
 RW>> dawned on them.

 DC> Though there was an attenpot to determine longitude purely by
 DC> celestial sightings, the only way to be accurate is with a proper
 DC> time piece.

Of course, but they didn't have that mechanism in 1492.

 DC>  An hour glass is not accurate enough.

It's pretty accurate. Not as accurate as a clock, but close enough to get
you where you want to go.

 DC> Besides it's inherent mechanical problems,

It only has one mechancial means and that is the use of gravity to feed
some grains of sand through a small hole. Maybe the glass is scratched so
that you can't see the sand go through the hole, but it will work out as
it will be visible on the bottom.

 DC>  there's the additional errors compounded by motion in a seaway.

Gravity still works at sea, even in high seas.

 DC> Also, there is the need to reset the hour glass as it runs through a
 DC> cycle.  It doesn't take much to introduce large errors in navigation.

Having a watch team to do nothing but turn the hour glass at the right
time won't lose enough time to make any big errors.

 DC>>> Try to figure out why such a large prize was offered for a
 DC>>> sea-going chronometer.

 RW>>> Even that isn't necessarily needed to navigate the oceans. It's a
 RW>>> great help, but not necessary.

 DC>> It's the only way to know exactly where you are.

 RW>> True, but it wasn't that important to have, until it came to be.

 DC> In one instance, the inaccuracy cost the British 4 ships of the line
 DC> and 2000 sailers and soldiers.  And, that was when the ships where
 DC> relatively close to home.

Oh well. That's called the mother of invention. There's always a better
way.

                R\%/itt



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