(Vitruvius names Cicero and Lucretius as post nostram memoriam nascentes.) The subjects of the eight chapters are - (1) the signs of the zodiac and the seven planets; (2) the phases of the moon; (3) the passage of the sun through the zodiac; (4) and (5) various constellations; (6) the relation of astrological influences to nature; (7) the mathematical divisions of the gnomon; (8) various kinds of sundials and their inventors.
He taught, if he did not discover, the obliquity of the ecliptic, is said to have introduced into Greece the gnomon (for determining the solstices) and the sundial, and to have invented some kind of geographical map. But his reputation is due mainly to his work on nature, few words of which remain.
His Lectiones in omnes Psalmos Davidis (1635) is exceedingly suggestive and terse in its style, reminding of Bengel's Gnomon, as does also his Commentarius utriusque Epist.
Nearly all sundials have a gnomon (which casts the shadow) pointing to the Celestial Pole.