The Nautical Encyclopedia

Patterson’s Illustrated Nautical Encyclopedia — Howard Patterson, 1891

⚓ The Superstition Locker ⚓

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Home ⚓ Letter S ⚓ Semi-diurnal Arc

Semi-diurnal Arc

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Half the diurnal arc-the part between the meridian and the horizon.

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The Nautical Encyclopedia (1891) is in the public domain; this digital edition © 2026 PhotoOpAI.