Zenith sector designed by Sir George Airy and used on Principal Triangulation from 1842-1850 Zenith sector, British, 1840 1840
Glass parts for Zenith sector designed by Sir George Airy and used on Principal Triangulation from 1842-1850 Part of Zenith Sector, British, 1840 1840
Main part of zenith sector designed by Sir George Airy and used on Principal Triangulation from 1842-1850 Part of Zenith Sector, British, 1840 1840