Engraving by Edward Harding after an earlier drawing by David Steuart Erskine. Gregory (1638-1675) invented the Gregorian reflecting telescope in 1661. The following year he published 'Optica promota' (The Advance of Optics), containing a description of his telescope. Gregory was profesor of mathematics at St Andrew's University and then at Edinburgh. Papers found after his death showed that he had anticipated the Taylor expansion and several other discoveries in number theory. Published in 1798. Dimensions: 370mm x 630mm.
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