Your favor of Nov. 19. arrived here just as I had set out for Bedford, from whence I returned a few days ago only, & found your letter here. I thank you for mr Lambert’s1 calculation on my observations of the late eclipse of the sun. I have been for some time rubbing up my Mathematics from the rust contracted by 50. years pursuits of a different kind, and thanks to the good foundation laid at College by my old master & friend Small, I am doing it with a delight & success beyond my expectation. I had observed the eclipse of Sep. 17. with a view to calculate from it myself the longitude of Monticello; but other occupations had prevented it before my journey. the elaborate paper of mr Lambert shews me it would have been a more difficult undertaking than I had foreseen, & that probably I should have foundered in it. I have no telescope equal to the observation of the eclipses of Jupiter’s satellites. but as soon as I can fit up a box to fix my instruments in, I propose to amuse myself with further essays to fix our longitude by the lunar observations, which have the advantages of multiplied repetitions & less laborious calculations. I have a fine theodolite & Equatorial both by Ramsden, a Hadley’s circle of Borda, a fine meridian and horizon as you know. once ascertaining the dip of my horizon I can use the circle, as at sea, without an artificial horizon. do you think of ever giving us a second edition of your map? if you do I may be able to furnish you with some latitudes. I have a pocket sextant of miraculous accuracy, considering it’s microscopic graduation with this I have ascertained the lat. of Poplar Forest, (say New London) by multiplied observations, & lately that of Willis’s mountains by observations of my own, repeated by my grandson, whom I am carrying on in his different studies. any latitudes within the circuit of these three places I could take for you myself, to which my grandson whose motions will be on a larger scale, would be able to add others. my unremitting occupations while you were engaged in the first publication put it out of my power to furnish you with some local draughts which might have aided you, to wit some very accurate surveys of James river from Cartersville about 10. miles upwards, some of the river in this neighborbood, some county lines, the country between New London & Lynchburg Etc. Accept my friendly salutations & assurances of great & continued esteem & respect.

Th: Jefferson