Within our own day and a short period of time preceding it, great improvements have been made in the construction of the pendulum-clock,[96] as well as in other descriptions of Chronometers.[97] Mr. Rittenhouse’s early zeal in his practical researches into astronomy, prompted him to desire the greatest possible accuracy in the construction of time-pieces adapted to astronomical purposes; and uniting, as he did, operative skill with a thorough knowledge of the principles upon which their construction depends, he was enabled—impelled by so powerful a motive—to display to the world, by his own manual ingenuity, the near approach to perfection to which the pendulum-chronometer may be brought. Besides his astronomical pursuits, his early employment in ascertaining the limits and fixing the territorial boundaries of Pennsylvania, and of some of the neighbouring states, obliged him to supply himself with chronometers of the greatest possible accuracy: and these were either made by his own hands, or under his immediate inspection by his brother, who, with the aid of his instruction, became an excellent mechanician. One of these fine instruments, bearing on its face the name of _Benjamin Rittenhouse_ as the maker, and the date of the year 1786, is now in the possession of Mr. Norton Prior,[98] of Philadelphia: but that admirable one, the workmanship of which was executed by our Philosopher himself, and which was part of the apparatus of his Philadelphia Observatory, is now placed in the hall of the American Philosophical Society.[99] This is constructed on a greatly improved plan of his own, which improvement was afterwards applied to that now belonging to Mr. Prior; and the latter is the same chronometer, it is believed, that was used by Mr. D. Rittenhouse, in fixing the northern line which divides Pennsylvania from New York, and in establishing the boundary line between the last mentioned state, and Pennsylvania and Massachusetts, respectively, in the years 1786 and 1787.—A description of the principles of his observatory-chronometer here mentioned, together with some account of its mechanism, will be found in the Appendix: the former having been communicated to the writer of these memoirs by the ingenious Robert Patterson, Esq. director of the Mint; and the latter by that able mechanician, Mr. Henry Voight, chief coiner in that institution,—a person who, by reason of his well-known skill as a clock and watch-maker, was employed by Mr. Rittenhouse more than forty years since, in the fabrication of some of his philosophical instruments. ----- Footnote 96: The first pendulum-clock made in England, was in the year 1662, by Mr. Fromanteel, a Dutchman.