Nautical Hemisphere

Invented by Michiel Coignet in 1581, the nautical hemisphere assumed the functions of the armillary sphere and the celestial globe. It allowed time to be measured directly. By using the different components of the nautical hemisphere triangles could be composed which allowed astronomical elevations to be calculated. On the basis of these one could calculate the times of high tide and low tide.

Robert Dudley depicted a similar instrument in his Arcano del mare (1661), which is now conserved in the Medicean collection of scientific instruments of the Museum of History of Science in Florence.

Mara Miniati
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