Thomas Jefferson Papers
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To Thomas Jefferson from Andrew Ellicott, 13 April 1801

From Andrew Ellicott

Philadelphia April 13th 1801

Dear Sir

I have accompanied this by a few sheets of my observations, they contain an account of the work on the boundary as far as to Pearl, or half-way river. The manner of describing the prime vertical as mentioned at the beginning of the line, I have not found noticed by any writer, but should think it too obvious to be new.—I am sorry the plate containing the references is not yet engraved.—

Whilst I was engaged in the City of Washington some years ago I made a number of observations to determine its longitude, but all of them with some papers relative to the plan of the City were lost, when the office was pillaged: But fortunately two very important observations had been communicated to our late worthy friend Mr. Rittenhouse, and published in the 4th. volume of the Transactions of our Society.—The first is on an annular eclipse of the Sun, and the second an occultation of (α ♉) Aldebaran by the moon.—Observations of this kind answer very well for the determination of the longitude, but the calculations are critical, and labourious, owing to the moon’s parallax in altitude, latitude, and longitude, and therefore not in common use:—However for want of other materials, and having little to do besides correcting the press, I have gone thro’ the calculations.—

The observation on the eclipse stands as below

D h  ′  ″
1791 April { Annulas completed at 2 18 35 45 } Apparent time { Observed at George
Annulas broken 2 18 39 57 Town
End of the eclipse 2 19 52 20 Lat. N. 38° 55’
h ′  ″
The Longitude by the completion of the Annulas is 5 7 53 } West from Greenwich
  do   by the breaking of the Annulas 5 8 14
  do   by the end of the eclipse 5 8 5

The second observation was made near the meridian of the
Capitol in latitude 38° 52′ 40″ N. and as follows.

D h  ′  ″
{ α ♉ immersed at 21 7 55 49.5 } apparent time
α ♉ emerged at 21 9 25 21.5
h ′ ″
Longitude by the immersion 5 7 13 } West from Greenwich
  do   by the emersion 5 7 47

The observation on the eclipse was made about 10” west from where the occultation was observed, which when deducted from the eclipse, the results will stand as below for the meridian of the Capitol.

h ′ ″
Longitude by the completion of the annulas 5 7 43 } West from Greenwich
  do   by the breaking of the annulas 5 8 4
  do   by the end of the eclipse 5 7 55
  do   by the immersion of α ♉ 5 7 13
  do   by the emersion of α ♉ 5 7 47
Mean 5 7 44.4 = 76° 56′ 6″

From which it appears, (in the language Americans ought to use), that Greenwich is 5h 7′ 44.4″ or 76° 56′ 6″ east from the City of Washington.—

I have been long wanting our longitudes to be reckoned, or counted, from our own Capitol, and not from a place within another country; and for this purpose calculated, and published an Almanac with the sun’s declination, eclipses of ♃trs. Satellites &c. adapted to the meridian of the City of Washington, which I had estimated at 5h 8′ west from Greenwich, but the plan fell thro when I left the City.—

We appear yet to be connected to Great Britain by a number of small ligaments, which tho apparently unimportant, are nevertheless a drawback upon that absolute independence we ought as a nation to maintain.—It would be very well when the longitude of the City of Washington is more accurately settled by a sufficient course of observations, consisting both of the eclipses of ♃trs. Satellites, and lunar distances, to have an American gazetteer published, in which the longitudes should be reckoned east, and west from the Capitol.—Wishing you health and happiness in discharging the important duties of your appointment, I am with sincere respect, and friendship, your Hbl. Servt.

Andw; Ellicott.

RC (DLC); at foot of text: “Thomas Jefferson President of U.S. and of the American Philosophical Society”; Ellicott used the astronomical symbols “α ♉” (“alpha Tauri,” which identifies the star as the brightest in the constellation Taurus) for the star Aldebaran and “♃” for the planet Jupiter; endorsed by TJ as received 24 Apr. and so recorded in SJL. Dft (DLC: Ellicott Papers). Enclosure not found; see Ellicott to TJ, 20 Mch.

Ellicott’s assertion that his office was pillaged referred to his acrimonious relationship with the commissioners of the Federal District before his departure from the surveying department in 1793. Elsewhere he stated that his information on eclipses of the moons of Jupiter had been “privately taken from my lodgings in Georgetown” along with some other notes. His figures on the 1791 solar eclipse observed at Georgetown and the 1793 occultation of Aldebaran by the moon appeared in the transactions of the American Philosophical Society in 1799 with data from several other astronomical observations (APS description begins American Philosophical Society description ends , Transactions, 4 [1799], 48–9; Bryan, National Capital description begins Wilhelmus B. Bryan, A History of the National Capital From Its Foundation Through the Period of the Adoption of the Organic Act, New York, 1914–16, 2 vols. description ends , 1:209–10; note to James Reed Dermott to TJ, 7 Mch. 1801).

Published an almanac: early in his career Ellicott was associated with the United States Almanack, and in the 1780s and early 1790s John Hayes of Baltimore issued Ellicott’s Maryland and Virginia Almanac (for examples, see Evans, description begins Charles Evans, Clifford K. Shipton, and Roger P. Bristol, comps., American Bibliography: A Chronological Dictionary of all Books, Pamphlets and Periodical Publications Printed in the United States of America from …1639 … to … 1820, Chicago and Worcester, Mass., 1903–59, 14 vols. description ends Nos. 19619, 23347, 22482; DAB description begins Allen Johnson and Dumas Malone, eds., Dictionary of American Biography, New York, 1928–36, 20 vols. description ends ).

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