The Accuracy of Angular Measuring Instruments Used in Astronomy between 1500 and 1850

Chapman Allan , Dividing the circle (Amersham, in press).

Of course, no one is claiming that Newton's work on the lunar theory was initiated by Flamsteed, although the important point remains that Newton required reliable observational ‘fixes’ if his theory was to be taken seriously as a true representation of nature. In 1690, the only instrument in Europe capable of providing such fixes to the requisite degree of accuracy, moreover, was the mural arc in the Royal Observatory.

Many references to the work of Gascoigne are extant; see Chapman , Dividing the circle. For primary sources, see Derham William , “Extracts from Mr Gascoigne's and Mr Crabtree's letters, proving Mr Gascoigne to have been the inventor of the telescopick sights of mathematical instruments, and not the French”, Philosophical transactions, xxx (1717), 603–10.

Hooke Robert , Some animadversions on the first part of Hevelius, his ‘Machina Coelestis’ (London, 1674), 7.