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Bill,

The answer to your first question is simple:

> 1. What ephemerial astronomical data was available
> to aid a sailor with a chronometer pre 1766?

There was no sailor with a chronometer before 1766 :-)
I mean there were 3 or 4 chronometers by Harison, but they were still
testing them...

And for long time after that, a sailor could not afford them.

> 2. How did a navigator check the accuracy of his chronometer
> before telegraph and time balls--especially at sea?

The time-ball in Greenwich is timed by astronomical clock.
The clock was checked by meridian observatons in the observatory.
Other balls in other places were probably introduced after the telegraph
was invented and underwater cables layed (1860-s).

Before this time there was no SIMPLE way to check chronometers,
except at certain places where there was an observatory
(London, Paris, Peterburg... I suppose).

Chronometers were also rare until mid XIX century.

Checking a chronometer was a major enterprise in the first half of XIX
century. One had to land, arrange a land observatory, etc.
I read how Russians did it in Japan in 1850-s...
(There was a problem with landing. Japanese authorities did not want
them to land, etc.)

Alex.

   

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