From William Lambert
Lancaster County, Virga June 24th 1814.
The reformation of the Julian calendar by pope Gregory XIII, in the year 1582, is so near the truth, that it will not want correction until 3600 years after the change of stile took place. It has been found by a series of observations noticed in Vince’s astronomy, that the tropical year is 365 days, 5 hours, 48 minutes, 48 seconds; if this be multiplied by 3600 years, the product will be 1,314,872 days, without the fraction of a second. In this period of 3600 years there will be 873 leap years and 2727 common years, which would make one day or 24 hours more than the product above mentioned; it will be necessary therefore, that the 3600th or some intermediate year, reckoned as Bissextile, should be made a common year; or in other words, that there must be 872 leap years and 2728 common years; for if we multiply 872 by 366 days, and 2728 by 365, the sum of the products will be 1,314,872 days, agreeing exactly with 3600 tropical years, according to the most accurate observations hitherto made. I wish to turn your attention and that of the American Philosophical Society to this subject, for altho’ the time is so far distant as not to affect many generations to come, yet I should be glad that the correction should be proposed in the United States of America, rather than in Europe, or any other part of the world.
RC (PPAmP: APS description begins American Philosophical Society description ends Archives, Manuscript Communications); addressed: “Honble Thomas Jefferson, late President of the United States, and President of the American Philosophical Society. Monticello”; stamped; postmarked Kilmarnock, 24 June; endorsed by TJ as received 8 July 1814 and so recorded in SJL; endorsed in an unidentified hand at APS description begins American Philosophical Society description ends : “Commn on Gregorian Callender read Augt 20. 1814 report. 7 Octr Enclosed.” Tr (DLC); entirely in TJ’s hand; abstract subjoined to PoC of TJ to Robert Patterson, 23 July 1814, and reading as follows: “The paper quoting Vince’s Astronomy for the tropical year being 365 d–5 h–48′–48″ observes that this will produce an error of exactly 1. day in 3600. years; because 365 D–5 H–48′–48″ × 3600 = 1,314,872 days within which are 873. leap years & 2727. common years, which would make 1. day more than the above number, to a single second. he proposes therefore that the 3600th year should be a common year because 872 × 366 + 2728 × 365 = 1,314,872 days.” Enclosed in TJ to Patterson, 23 July 1814.
This letter was read at a meeting of the American Philosophical Society on 19 Aug. 1814 and referred to a committee consisting of John Gummere, Robert Patterson, and Jonathan Williams. On 7 Oct. 1814 the society accepted the committee’s recommendation that Lambert’s communication “be filed among the papers of the Society” (APS description begins American Philosophical Society description ends , Minutes [MS in PPAmP]).
Lambert took the observations from Samuel vince’s book entitled A Complete System of Astronomy (Cambridge, Eng., 1797), 52–7. bissextile: a leap-year, or the extra day that the Julian calendar adds to it (OED description begins James A. H. Murray, J. A. Simpson, E. S. C. Weiner, and others, eds., The Oxford English Dictionary, 2d ed., 1989, 20 vols. description ends ).
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