The object of this communication was to shew that, by the use of metallic reflectors for sextants, greater accuracy was obtained in the observed angles, and also that larger angles could be observed. Objects were seen reflected by metallic mirrors, which could not be seen when glass was used; and that when the alloy was formed of pure metals, it was not subject to rust or tarnish, even when exposed to action of the sea air.

The author then exhibited a sextant fitted with these mirrors, which had been employed for a season in the survey of the north coast of Scotland, under Mr Mossman, and read extracts of letters from that gentleman.