Secchi disc noun phr. ['sɛkɪ dɪsk] Also Secchi's disc ['sɛkɪz], *Secchi disk, Secchi's disk. E20.
[Angelo Secchi (1818-78), Italian astronomer.]
An opaque white disc used to gauge the transparency of water by measuring the depth at which the disc ceases to be visible from the surface.

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