1851 Great Exhibition: Official Catalogue: Class X.: George Heath
351. HEATH, GEORGE, Erith, Kent — Manufacturer.
Solid bell-metal ivory arched sextant, divided to 10 seconds, combining the clearness of ivory with the durability of metal. Owing to the extreme minuteness of the divisions on instruments divided to 10 seconds, the difficulty of reading them off is great. This is obviated by the use of ivory, as a black mark on a white ground presents a much greater contrast than a self-coloured mark on metal.
Improved action magnifier. In other instruments, the magnifier placed to facilitate the reading off the divisions moving in a smaller circle than the arch, distorts the divisions upon approaching the extremity of the vernier, by their being thrown out of the centre of the lens. This is avoided by the present plan.
Improved spring hollow leg, thus to avoid the possibility of altering the adjustments of the instrument in placing it down.
Improved ivory arch metal quadrant, possessing, in respect to the ivory, the qualifications of the before-mentioned sextant: the ivory being dovetailed into the metal, cannot come out or shrink.