Gregory's meridian line of 1673–74: a St Andrews detective story

Abstract

In 1668, James Gregory arrived in St Andrews University following his two-year sojourn at Padua University. He planned to create the first purpose-built astronomical observatory in Britain to take celestial measurements to a new level of accuracy superior to anything else in Europe. In 1673 he had assembled an enviable collection of astronomical instruments and time-keepers of unusually high quality and precision. By the following year he had converted the upper floor of the Old Library into his observatory and constructed the first ever non-ecclesiastical astronomical meridian line in Europe, the longest and most accurate of its kind for many years to come. Recent site surveys and computations by the author show that ‘Gregory's pillar’, the south mark for his meridian line, is less than 1 metre to the side of the terrestrial geodetic meridian through the telescope bracket in the window of Upper Parliament Hall 2.4 kilometres to the north. What technical methods did Gregory use to achieve what he did? What depths of academic prejudice destroyed his hopes? The author outlines the little that is known and takes the first steps towards unravelling a three-centuries old mystery.

Acknowledgements

This paper is a much enlarged version of an article commissioned by Anne J M Morris OBE, Chair of the St Andrews Preservation Trust, for inclusion in the Trust's Annual Report 2005. Helen Rawson, Curator of St Andrews University's Museum Collections, provided important and useful insights. Valuable historical and technical information about Gregory and Cassini was found in the St Andrews Mactutor website maintained by Edmund Robertson and John O’Connor: http://www-groups.dcs.st-and.ac.uk/∼history/Mathematicians/Gregory.html

The photographs inside Upper Parliament Hall were taken by the author and reproduced with the permission of Professor Ian Carradice, Keeper of the University's Museum Collections. All other photographs were taken by the author in his own right.

The extract from the old Ordnance Survey map is reproduced courtesy of the Map Collection of the National Library of Scotland.

The help of the St Mary's College Janitors with taking up the carpets to reveal the inlaid 1747 meridian line is gratefully acknowledged.