12. An Optical Problem, proposed by Mr. Hopkinson, and solved by Mr. Rittenhouse. Read, Feb. 17. 1786. (N. B. Mr. Hopkinson’s letter is dated March 16, 1785: the answer is without date.) 13. Astronomical Observations; communicated by Mr. Rittenhouse. Without date.[329] ----- Footnote 329: These observations were made in Philadelphia, by Dr. Rittenhouse, at sundry times in the years 1784, 1785, and 1786, on the new planet, or Georgium Sidus; and on the Transit of Mercury over the Sun’s disk, on the 12th of November, 1782. The same communication also states the geocentric places of the Georgium Sidus, at several different dates between the 1st of April, 1762, and the 14th of March, 1784, both included; as observed by Mr. James Six, at the city of Canterbury in England. ----- 14. The third volume, printed in the year 1793, contains—An Account of several Houses, in Philadelphia, struck with Lightning on the 7th of June, 1789; by Mr. D. Rittenhouse and Dr. John Jones. Read, July 17. 1789. 15. An Account of the Effects of a stroke of Lightning on a House furnished with two Conductors; in a letter from Messrs. David Rittenhouse and Francis Hopkinson, to Mr. R. Patterson. Read, October 15. 1790. 16. Astronomical Observations made at Philadelphia: viz. of a Lunar Eclipse, on the 2d of November, 1789; of the Transit of Mercury over the Sun’s disk, on the 5th of November, 1789; of an Eclipse of the Moon, on the 22d of October, 1790; of an Eclipse of the Sun, on the 6th of November, 1790; and of an Annular Eclipse of the Sun, on the 3d of April, 1791:[330] with an Account of corresponding Observations of the two first of these Phænomena, made at the University of William and Mary in Virginia, by the Rev. Dr. Madison; and of the second, alone, made at Washington-College in Maryland, by the Rev. Dr. Smith: communicated by D. Rittenhouse. Read, February 4. 1791. ----- Footnote 330: This eclipse was observed by Andrew Ellicott, Esq. at the city of Washington, as follows; viz. { 6.^h 39′. 1″,25 } Annulus completed } April 3d. { 6. 43. 15,25 } Do. broken } M. Time. { 7. 55. 37,75 } End of Eclipse. } A letter from the celebrated French Astronomer, Lalande, to Dr. Rittenhouse, on the same subject, has been already given. ----- 17. A Letter from Dr. Rittenhouse to Mr. Patterson, relative to a Method of finding the Sum of the several Powers of the Sines, &c. Read, May 18. 1792. 18. An Account of a Comet, (first observed by Mr. Rittenhouse, on the 11th of January, 1793:) in a letter from D. Rittenhouse to Mr. Patterson.[331] Read, February 15. 1793. ----- Footnote 331: