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Thank you for your comments:

1) My apologies - it is 1421 not 1491. Typo error. And yes it is 1421 the
Year China Discovered the World. My heading was just a bit of tongue in
cheek.

2) Both George Huxtable and Antonio Canas point out that the theory and
practice of finding longitude by observation of eclipses was well known. I
have no argument with this view. Menzies assertion however is that the
Chinese by 1421 had used the technique to remarkable effect mapping most of
the known world with extraordinary precision, placing virtually all the
worlds continents in their exact cartographical positions. Eg he asserts
that the East Coast of Australia had been mapped by this time, centuries
before the Portuguese and English arrived here. He assets that the Venetian
Marco Polo may have taken some of these charts back to Europe where they
were eventually acquired by the Portuguese (Prince Henry the Navigator) and
later the English.

He repeats the oft-made claim, which I support, that James Cook had a
Portuguese chart on the Endeavour when he arrived on the Australian East
coast and that his chart had been copied from an earlier Chinese chart. (The
latter part of that thesis may be a bit of a stretch.)

It is not the theory I was questioning it was the practice.


3)      Trevor Kenchington and George gave a very through explanation of how the
observation could have been done in practice, which was very enlightening.
However I am still a bit curious as to how time was measured and whether
Menzies water clock would have been accurate enough. Trevor went on to say:

"Were Chinese eclipse predictions at the time accurate enough for people to
know which Full Moon would have an eclipse or did our hypothetical explorers
have to sit around, month after month, waiting against the day
when the Earth's shadow would cross the Moon's disc?"

This was the reason for my query about the requirement for an accurate
Nautical Almanac. The Menzies hypothesis  presumes a very advanced level of
predictive ability in the Chinese astronomers.

3) Trevor also wrote:
"But just because the Chinese of the 15th century ..... could have, or even
did, determine longitudes from eclipses would not itself demonstrate that
they fixed the locations of anywhere outside the well-known range of Chinese
voyaging in the decades before the Ming Ban. That would need a quite
different kind of evidence."

It is the evidence of the maps themselves that Menzies is holding up for
scrutiny. The existence of these very accurate and detailed maps of
Magellan's Passage, Greenland and the east cost of America centuries before
Europeans arrived would I believe require some rewriting of history.


Thanks for the assistance. At least we know it may have been possible for
the Chinese to calculate longitude on land when they did. I remain a sceptic
about a lot of Menzies claims but ever since I was a child I have wondered
how Magellan knew there was a straight at the bottom of South America that
he could sail through to get to the Pacific Ocean. If nothing else, Menzies
supplies one possible explanation.

Kieran Kelly
Sydney
Australia'

   

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