Two-inch-thick fir planks were used to build a cask with valves at each end linked to a horizontal lever with a flat circular paddle; lowering pushed the lever to open valves and admit seawater into the barrel, and stopping descent caused valves to close so the paddle kept the barrel sealed during retrieval. Scoresby first deployed the fir-cask on April 19, 1810 from the Resolute near Svalbard. Surface water at 28.8°F measured in April was colder than trapped samples from 300, 738, and 1,380 feet, which measured 31.8°F, 33.8°F, and 33.3°F respectively. Thermometer placement was adjusted and measurements repeated into 1811 with similar results.
The cask was made of two-inch-thick fir planks, "as being a bad conductor of heat." At each end of the cask was a valve connected by a wire that opened and closed at the same time-a horizontal lever with a flat circular paddle extended from the barrel. When lowered, the lever was pushed upward, opening the valves and allowing seawater to flow through the barrel.
The conventional wisdom was, and remains for many today, that the ocean is like a big bathtub where the temperature you feel with your toe correlates to the temperature down in the water column. If anything, the water would become colder with depth due to increasing distance from the surface and increasing density with rising pressure from the column of water above.
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