This is a Portuguese maritime treatise on spherical and planetary astronomy, based on the Ptolomeic system, but with presentation of the Copernican system. There are numerous diagrams and a few interesting sketches.

This volume was made at Wilmington, Delaware, for determining the longitude, from 1 July-14 October. It records the position of selected stars and planets. Contains also: Note regarding his astronomical clock, and entries relative to his work in continuing the Mason & Dixon's line.