LWS 1197, Thomas Jefferson to John Payne Todd, October 10, 1811
(referring to September 17, 1811 solar eclipse)
To John Payne Todd
Monticello Oct. 10. 11.
According to promise I send you our observations of the solar eclipse of Sep. 17. we had, you know, a perfect observation of the passage of the sun over the meridian, and the eclipse began so soon after as to leave little room for error from the time piece. her rate of going however was ascertained by 10. days subsequent observation and comparison with the sun, and the times, as I now give them to you are corrected by these. I have no confidence in the times of the 1st & ultimate contacts, because you know we were not early enough on the watch, decieved by our time piece which was too slow. the impression on the sun was too sensible when we first observed it, to be considered as the moment of commencement, and the largeness of our conjectural correction (18″) shews that that part of the observation should be considered as nothing. the last contact was well enough observed, but it is on the forming and breaking of the annulus that I rely with entire confidence. I am certain there was not an error of an instant of time in either. I would be governed therefore solely by them, and not suffer their result to be affected by the others. I have not yet entered on the calculation of our longitude from them. they will enable you to do it as a college exercise. affectionately yours
|annulus formed||1–||53–||0||central time||H ′ ″||central time||H ′ ″|
|annulus broken||1–||59–||25||of annulus.||1–56–12½||of the two contacts||1–51–28|