1From Benjamin Franklin to Peter Collinson, 5 November 1756 (Franklin Papers)
...S., 1737; recognized as the foremost maker of glass specula of his day.
2From Thomas Jefferson to Francis Hopkinson, 3 January 178[6] (Jefferson Papers)
...as the metal hitherto used, for the specula of telescopes. These two properties had...
3From Thomas Jefferson to David Rittenhouse, 25 January 1786 (Jefferson Papers)
...polish as the metal heretofore used for the specula of telescopes, is inattackable by rust as...
4From Thomas Jefferson to Benjamin Franklin, 27 January 1786 (Jefferson Papers)
...thought of using the metal Platina for the specula of telescopes. Indeed I believe the thought...
5From Thomas Jefferson to James Currie, 28 January 1786 (Jefferson Papers)
...called Platina to the purpose of making the specula of telescopes. It is susceptible of as...
6From Thomas Jefferson to Ezra Stiles, 1 September 1786 (Jefferson Papers)
...of the mixed metal of which the specula were formerly composed. It is insusceptible of...
7To Thomas Jefferson from John Ledyard, 19 March 1787 (Jefferson Papers)
...I saw the reason—the true reason in the specula of the secretarys eye—and so damn his eyes—...
8Remarks on Observations with a Sextant, 18 April 1803 (Jefferson Papers)
...true, will be fainter than that from the specula, unless the Telescope of the Sextant be...
9John Vaughan to Thomas Jefferson, 19 April 1813 (Jefferson Papers)
Observationes siderum habitae Pisis in specula academica (Slop von Cadenberg) [index entry] specula
10Thomas Jefferson to John Vaughan, 24 April 1813 (Jefferson Papers)
...describing them as “Observationes Siderum habita Pisis in Specula Academica ab ano 1778 ad...
11Thomas Jefferson to Robert Patterson, 13 October 1815 (Jefferson Papers)
or the mixt metal of the telescopic specula, or even of common glass mirror, with cross
12Robert Patterson to Thomas Jefferson, 28 November 1815 (Jefferson Papers)
...brightness with that made by a double reflection from the specula of the sector.
13Thomas Skidmore to Thomas Jefferson, 18 August 1822 (Jefferson Papers)
...is “an alloy of copper and tin used for making specula” (