Appendix: The dating of Troughton instruments

INSTRUMENTS made by John and Edward Troughton, alone or in partnership, were signed ‘Troughton London’ throughout the whole of the period 1782 to 1826. Consequently, the need arises for establishing chronological information and methods by which the date of any particular instrument can be fixed within much closer limits. Some instruments carry a maker’s date, others can be dated from specific documentary evidence. Sextants of the ‘pillar’ type, and Reflecting Circles, are numbered serially and can be dated by means of correlations based on the data assembled in Notes (K) and (L). Trade cards may provide useful information, and typological considerations are obviously important. The maker’s signatures engraved on the instruments are also worth noting.