Mr. Francis de Zach (Astronomer to the duke of Saxe-Gotha,) in the explanation and use of his table, No. 38, entitled, “Correctio horæ meridianæ prodeuntis ex altitudinibus correspondentibus Solis,” says—“Tradit Clarissimus DAV. RITTENHOUSE, in Transactionibus Americanis (vol. 1. p. 155. edit. 2.), Methodum novum correctionis horæ meridianæ, absque tabulis, ex solâ observatione deducendæ; sed requiruntur, ad hoc, duorum dierum subsequentium altitudines quatuor æquales: id est, sub eadem altitudine manè et vesperi factæ, ad assequendam ex his, correctiones meridiei, Regulæ Clariss. Authoris sunt sequentes:” Mr. de Zach then lays down Dr. Rittenhouse’s Rules, which will be found in the Transactions of the American Philosophical Society, already referred to; and adds—“Exempla hoc perspicuum reddent:” he next states two examples, from which he deduces proofs of the accuracy of Dr. Rittenhouse’s method. See “_Tabulæ Motuum Solis, novæ et correctæ, ex Theoriâ Gravitatis et Observationibus recentissimis erutæ, &c. auctore Francisco de Zach_:” printed at Gotha, in 1792. ----- 6. Account of the Terrestrial Measurement of the difference of Longitude between the Observatories of Norriton and Philadelphia; drawn up by the Rev. Dr. Smith, in behalf of Mr. Lukens, Mr. Rittenhouse and himself, the committee appointed by the Am. Philos. Society, for that purpose, agreeably to the request of the Astronomer-Royal of England. Dated, Aug. 17. 1770. 7. The second volume, printed in the year 1786, contains—An Explanation of an Optical deception. Read, March 3. 1780. 8. An Account of some Experiments on Magnetism; in a letter from Mr. Rittenhouse to John Page, Esq. of Williamsburgh. Read, Feb. 6. 1781. 9. A letter from David Rittenhouse, Esq. to John Page, Esq. in answer to one from Mr. Page;) concerning a remarkable Meteor, seen in Virginia and Pennsylvania, on the 31st of Oct. 1779. Read, May 2. 1783. (N. B. Mr. Rittenhouse’s letter is dated Jan. 16. 1780.) 10. Observations on a Comet lately discovered; communicated by David Rittenhouse, Esq.[328] Read, March 19. 1784. ----- Footnote 328: This Comet was observed by John Lukens, Esq. of Philadelphia, on the 20th of January, 1784. This respectable practical astronomer communicated his discovery of it to Dr. Rittenhouse the next day, on the evening of which, (“assisted by Mr. Lukens and Mr. Prior,”) he ascertained the then apparent place of this comet. Dr. Rittenhouse’s communication to the society, on this subject, gives also the apparent place of the comet on the 17th of February, being the last time the weather permitted him to see it: the result of his intermediate observations is also stated. ----- 11. A new Method of placing the Meridian Mark; in a letter to the Rev. Dr. Ewing, Provost of the University. Read, November. 1785.