zenith tube

American  

noun

Astronomy.

1. a telescope mounted to point only at the zenith, used at some observatories for measuring time by the stars.

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Etymology

Origin of zenith tube

First recorded in 1830–40

Example Sentences

He devised a reflex zenith tube, in which the zenith point was determined by reflection from a surface of mercury.

From History of Astronomy by Forbes, George

The instrument is now being used for investigating these variations; and in the year 1907 as many as 1,545 observations of stars were made with the reflex zenith tube.

From History of Astronomy by Forbes, George

In 1848 Airy invented the reflex zenith tube to replace the zenith sector previously employed.

From The Project Gutenberg Encyclopedia Volume 1 of 28 by Project Gutenberg