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Bradley had a zenith sector, and with this he observed with the greatest care the zenith distance of Gamma Draconis at every possible opportunity.

This figured out the size of the earth with a percentage of error surprisingly small when we consider the rough means with which Eratosthenes measured the sun's zenith distance and the distance between the two stations.

Form used in the computation of the zenith distance and azimuth of the moon.

A case is noted in the Indian survey where the zenith distance of a station 10.5 miles off varied from a depression of 4′ 52″.6 at 4.30 P.M. to an elevation of 2′ 24″.0 at 10.50 P.M.

To take an example: the mean of eight observations of the zenith distance of the sea horizon at the top of Ben Nevis is 91� 4′ 48″, or δ = 64.8; the ray is pretty equally disposed over land and water, and hence h = 1.047n�