secchi disc A disc used in a simple method for measuring the transparency of water. The disc is 20 cm across and divided into alternate black and white quadrants. It is lowered into water on a line until the difference between the black and white areas just ceases to be visible, at which point the depth is recorded. The secchi disc provides a convenient method for comparing the transparency of water at different sites. The disc was invented by the Italian Jesuit and eminent astrophysicist Angelo Secchi (1818–78).

secchi disc A disc used in a simple method for measuring the transparency of water. The disc is 20 cm across, and divided into alternate black and white quadrants. It is lowered into water on a line until the difference between the black and white areas just ceases to be visible, at which point the depth is recorded. The secchi disc provides a convenient method for comparing the transparencies of water at different sites.

Secchi disc A device used in a simple method for measuring the transparency of water. The disc is 20 cm across, and divided into alternate black and white quadrants. It is lowered into the water on a line until the difference between the black and white areas just ceases to be visible, and this depth is recorded. The Secchi disc provides a convenient method for comparing the transparencies of water at different times.