In this letter, Dr. Rittenhouse merely informs Mr. Patterson, in general terms, of the time when he first observed this comet, its then place, and its course through several of the constellations, until the 8th of February; on the evening of which day, he saw it for the last time. It is presumed that Dr. Rittenhouse’s state of health, at that period, would not admit of his making more definite observations on this comet. ----- The fourth volume, printed in the year 1799, (three years after Dr. Rittenhouse’s death,) contains— 19. A paper, “On the Improvement of Time-keepers;” by David Rittenhouse, LL. D. Pres. Am. Philos. Society. Read, November 7. 1794.[332] ----- Footnote 332: This _desideratum_ in astronomical science had long engaged Dr. Rittenhouse’s attention; and it is confidently said by one of his intimate friends, that, in the latter part of his life, he had actually written much on the subject of Pendulums; intended, probably, for publication. But, unfortunately, the manuscript-book, which contained what he had thus written, can not now be found. In the paper mentioned in the text, he remarks, that “the invention and construction of time-keepers may be reckoned among the most successful exertions of human genius. Pendulum-clocks especially,” says he, “have been made to measure time with astonishing accuracy; and, if there are still some causes of inequality in their motions, the united efforts of mechanism, philosophy and mathematics, will probably, in time, remove them.” Indeed no man has done more, none perhaps so much, towards removing the imperfections in chronometers, to which he alludes, as this great mechanician himself. His admirable time-piece, now in the possession of the Philosophical Society at Philadelphia, constructed by him, on an improved plan of his own, affords ample proof of the “astonishing accuracy” (as he expresses it) to which the pendulum-chronometer may be brought. A description of the mechanism of this extremely accurate time-piece, as well as of the principles on which its superior correctness depends, is inserted in the Appendix. ----- 20. A paper, “On the Expansion of Wood by Heat;” in a letter from David Rittenhouse, LL. D. Pres. Am. Philos. Society. Dated, May 15. 1795. 21. A Method of raising the common Logarithm of any number immediately; by D. Rittenhouse, LL. D. Pres. Am. Philos. Society. Read, August 12. 1795. 22. A communication, “On the Mode of determining the true Place of a Planet, in an eliptical Orbit, directly from the mean Anomaly by Converging Series;” by David Rittenhouse, Pres. Am. Phil. Society. Read, February 5. 1796. --- This last communication was made to the Society, within five months of the time immediately preceding Dr. Rittenhouse’s death.