Barometers
Knowing where you were and where you were going was only part of the essence of seafaring, because steering into a storm, or, alternatively, into a calm, could be fatal. The early nautical barometers of the 1800s are unlike what you'd expect, especially if you're used to having a round barometer and wall clock as a matched set.

Early barometers were tall and stick-like, with the mercury reading taken against an ivory scale, set in a case often ornately carved from mahogany, rosewood, or other exotic woods. Frequently combined with the barometer was a sympiesometer, which used alcohol and hydrogen gas rather than mercury to measure barometric pressure, and a thermometer was commonly found on the gimbaled barometer "stick."

Because of the fragility of barometers, the stick style from the 1800s is both rare and expensive, often in the $9,000 to $12,000 range depending on the condition and provenance.

An interesting sidenote: most English barometers had only pressure readings, while American barometers simplified matters by adding the "Fair-Change-Rain-Dry" indicators.