“The Spectacles suit my eyes extremely well—as I am persuaded the Reading-Glasses also will, when I get more accustomed to the use of them. At present, I find some difficulty in coming at the proper focus; but when I do obtain it, they magnify perfectly, and shew those letters very distinctly, which at first appear like a mist—blended together and confused. With great esteem and respect, I am, Sir, your most obedient and humble servant, “GO. WASHINGTON. “DAVID RITTENHOUSE, Esq.” The grinding and polishing of the glasses were of Mr. Rittenhouse’s own workmanship; and they were made for the purpose. This circumstance, added to the manner and occasion of their being presented, could not fail of being highly acceptable to the General. In the year 1784, Mr. Rittenhouse was employed on the part of Pennsylvania, for the purpose of determining the western extension of that state; and was associated in that business with Mr. Lukens, Dr. Ewing, and Capt. Hutchins: the commissioners in behalf of Virginia were Dr. (afterwards bishop) Madison, Mr. Ellicott,[213] Mr. J. Page, and the Rev. Mr. R. Andrews. A record of the astronomical observations which were made on this occasion, and on similar ones of an important nature, will be found detailed in a letter, under the date of April 2, 1795, addressed by Mr. Ellicott to Mr. Patterson, in the fourth volume of the Am. Philos. Society’s Transactions. Among the observations contained in the first part of that letter, are those of the immersions of the satellites of Jupiter, taken at Wilmington on the Delaware, by Messrs. Rittenhouse, Lukens, Page and Andrews, at divers days from the 1st to the 23d of August, in the year 1784; together with those taken at the western observatory by Messrs. Ellicott, Ewing, Madison and Hutchins, at divers days from the 17th of July to the 19th of August; also, the emersions of those satellites by the same eastern observers, from the 29th of August to the 19th of September; and by the same western observers, from the 27th of August to the 19th of September; all in the same year. ----- Footnote 213: Although Mr. Ellicott is a native of Pennsylvania, and was a citizen of that state until the British army took possession of Philadelphia, in 1777, he resided in Baltimore county about eight years after that event. ----- “After the determination,” says Mr. Ellicott, “we completed the southern boundary of Pennsylvania; it being likewise the north boundary of Maryland, and a part of Virginia; and which had been carried on some years before,[214] by Messrs. Mason and Dixon, the distance of 242 miles.” This line is in the parallel of 39° 43′ 18″ North latitude.[215] ----- Footnote 214: In the years 1767 and 1768. Footnote 215: