Secchi disk

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an opaque, white or black-and-white disk used to measure the cloudiness or turbidity of ocean water by the point at which it is no longer visible from the surface.
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Origin of Secchi disk

First recorded in1910–15; named after Pietro Angelo Secchi (1818–78), Italian astronomer who invented it in 1865

Words nearby Secchi disk

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Scientific definitions for Secchi disk

Secchi disk

An instrument used for measuring the clarity of water, especially seawater. It consists of a circular plate divided into alternating black and white quadrants and attached to a long measuring tape. The plate is lowered into the water, and the depth at which it is no longer visible from the surface is recorded. The Secchi disk is named after its inventor, Italian astronomer Angelo Secchi (1818-1878). See also Secchi depth.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.