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Thanks to Dave Walden for supplying an extract from Maskelyne's "Tables
Requisite", 2nd edition, 1781; the page which contained that impossible
lunar, for which the lengths of the three sides are incompatible with any
triangle. Indeed, those sides, and the angles that give rise to them, are
almost identically copied in a later example, set by John Hamilton Moore,
and appearing from the 9th edition (1791) of his Practical Navigator. Some
small changes have been made to the odd arc-minutes in the observations,
perhaps to evade allegations of direct copying.

Moore's version allows for the Moon's HP to be interpolated to a particular
moment in time, for which he provided a longitude by account and a
watch-time. Unfortunately, these turn out to be incompatibe with other
aspects of the problem, giving rise to a further impossibility. That
example was repeated in at least two later editions.

George.

contact George Huxtable, at  george@hux.me.uk
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

   

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