Govaert Wendelen · 1626
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Govaert Wendelen (Godefridus Wendelinus, 1580–1667) was a Flemish priest and astronomer. Loxias, “the oblique one,” an epithet of Apollo, is his treatise on the obliquity of the ecliptic: the angle between the Sun’s annual path and the celestial equator.
Wendelen opens with the observations of his predecessors, from Eratosthenes and Ptolemy through al-Battānī, al-Zarqālī, Peuerbach, Copernicus and Tycho, to his own measurements at Forcalquier in Provence between 1609 and 1612. From Eratosthenes to Peuerbach he finds a steady decrease; after Peuerbach the figures rise and fall. He concludes that the obliquity is not fixed, and in seven chapters works out a rule for its variation. The book closes with a table of the solar obliquities and instructions for its use.
Loxias is an early landmark in the long debate over whether, and how, the obliquity changes.
The source is the 1626 printing, from a copy in the Hendrik Conscience Heritage Library, Antwerp, digitized by Google Books.