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George,

Thank you for your comments. I have only two small remarks to them:

The simultaneous use of the easterly and westerly distance was possible even 
if the Sun was used for one of them. For example, you can take a westerly 
distance to the Sun two hours before the sunset and an easterly distance to a 
star during the subsequent twilight. The oldest almanac editions tabulated 
the star distances together with the opposite Sun's distances for days, when 
it was necessary. Only a good timepiece, not a chronometer, was needed to 
establish the time interval between such two observations that was necessary 
for evaluating the average result. Of course, the problem of irradiation was 
more sensible in such cases in comparison to two star distances.

Your remarks about captain Cook's practice of lunars are extremely 
interesting. Only from you I hear that the purported triumph of chronometer 
in Cook's hand is rather the result of the deliberate propaganda or the dull 
repetition of unverified assertions lasting for century(ies).

But Cook's use of lunars on land between individual legs of the voyage that 
you mention was needed only in the earliest times. After the longitudes of 
many ports had been reliably determined (with the accuracy sufficient for the 
ordinary navigation), other and more accurate methods (albeit astronomical 
ones before local time signals has been established) were commonly used for 
ascertaining the error of chronometers (and their rate too, which was 
impossible by lunars). I refer to time sights and corresponding altitudes 
above the artificial horizon, of course.

With many greetings


Jan Kalivoda

   

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