De principiis astronomiae et cosmographiae, (only in the 3th edition of 1553)
Gemma Frisius, Leuven
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In this work, and only in this 3rd edition of 1553, Frisius refers to the use of a ‘portable timekeeper’ for determining longitude at sea.
In other words, the principle of the marine chronometer was already known in the 16th century.
Third edition of 1553, the first published in 1530, of Gemma Frisius' great work on the principles of astronomy and cosmography, with instructions for the use of terrestrial and celestial globes, and information about the world, islands, and other newly discovered places. With the last two chapters dedicated to America. This edition is very important because it is the first in which the treatise has been added on pp 64-65 " De novo modo inveniendi longitudinem " (chapter XVIII or De usu globi, in Gemma's De principiis astronomiae et cosmographiae, Antwerp, 155341, in which he proposes in explicit terms the use of portable clocks to measure longitude by elapsed time. In fact, it describes for the first time how the longitude of a place can be found by using a clock to determine the difference in local and absolute times (200 years before Harrison developed his chronometer H1 in 1730).
The work is divided into three parts: The first describes its geographical and astronomical theorems and defines the terms latitude, longitude, meridians, poles, eclipses, position of the stars, etc. The second part is devoted to the sphere and its use, of great importance for shipping at the time; the third volume in a treatise on the ethnography and natural history of the East and West Indies, of interest to America.