A-275. The mariner's astrolabe was once a common navigational instrument, used to measure the altitude of the sun or a star. It was usually made of thick metal and pierced with large openings, for stability while making observations in the wind. This Portuguese instrument is dated 1616, and is one of only a few dozen in the world that have survived (apparently most were discarded, or lost at sea).

A-249. This sextant, signed "B. Biggs, Cardiff," was made in Cardiff, New York, in the early 19th century.