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.

This journal was found among the papers of Benjamin Smith Barton, who was Pursh's patron, after his death in 1817. For provenance of manuscript see ms. notes in printed edition by Thomas P. James - 581.974:P97.

The first volume contains notes of expenses and of observations while surveying the western boundary of Pennsylvania (1785). Mentions APS under date of Feb. 20, 1784. The second volume contains observations that were continued after Rittenhouse's death to Sept. 30, 1805.