An APPENDIX,—containing sundry letters and other papers, which could neither be incorporated with propriety into the text, nor inserted in marginal notes,—is placed after the conclusion of the Memoirs. In this part of the work the reader will find, among other interesting documents, Dr. Rittenhouse’s _Oration_ on the subject of Astronomy, pronounced before the American Philosophical Society, in the year 1775. The addition of this treatise to the Life of our Philosopher, was rendered the more proper,—independently of the intrinsic merit of the performance,—by reason of the pamphlet having had, originally, a very limited circulation, and its being now out of print. The Notes, added to this little tract, as well as to some other papers in the Appendix, by the Memorialist, are designated by the initials of his name; in order to distinguish the annotations from either the notes originally attached to them,—or from other matter, in the Text, not written by himself. The author has embellished his work with an elegantly engraved likeness of Dr. Rittenhouse, executed by an able artist, from a portrait painted by Mr. C. W. Peale, in-the year 1772,[I2] when our Philosopher was forty years of age. At that time he wore a wig,—and was so represented in the picture: but afterwards, when he resumed the wearing of his own hair, (and which he continued to do during the remainder of his life,) the portrait was altered accordingly, by Mr. Peale. The original picture (now in the possession of Mrs. Sergeant,) bore a strong resemblance to Dr. Rittenhouse, at that period of his life in which it was taken; and the engraving, prefixed to these Memoirs, is an excellent copy. ----- Footnote I2: Mr. C. W. Peale painted at the same time another portrait of him, for himself; which is likewise altered from the original painting. It has a place in Mr. Peale’s Gallery of Portraits. There is a third, by the same hand, in the possession of the American Philosophical Society. Another good picture of Dr. Rittenhouse was also then made, by Mr. James Peale, for the Rev. Mr. Barton. This (which represents him with a wig) is now in the possession of John Moore White, Esq. of New-Jersey, who married Mr. Barton’s youngest daughter. A pretty good mezzotinto, in a large size,—done from Mr. C. W. Peale’s painting of our Philosopher,—was executed by Mr. E. Savage, in the winter of 1796: and since that time, some small engravings have been made from different pictures of him; but these do not so well preserve the likeness. -----