Thomas Jefferson Papers

To Thomas Jefferson from William Dunbar, 9 July 1805

Natchez 9th. July 1805

Dear Sir

I have received the honor of your letter of the 25th. May, as also your note covering a letter for the Chevalr. Dannemour, which last has been forwarded. Having been of late engaged with my private concerns, my attention has been suspended from objects of a different nature, otherwise I should have, ere now, completed my sketch of the course of the Washita river, but I shall certainly get it prepared & forwarded long before the meeting of the Legislature. The alteration you have been pleased to make in the ensuing expedition, so that one river only shall be explored at time will greatly facilitate the business; it will be infinitely more convenient and safe, and perhaps both time and expence will be saved. Mr. George Davis was mentioned by me last year to the Secretary at war; tho’ not fully qualified, I thought him the best we could then procure, & that with good instructions he might do; but since that time Mr. Briggs and myself have both discovered that he is a very unfit person; he is of so unhappy a disposition, that we cannot think, any harmony would exist in the party where he might be placed even in a subaltern character, much less were he in authority. He has the merit of possessing some self acquired mathematical knowledge, but no practical knowledge as an astronomer. He has been a Deputy of Mr. Briggs to the present time, and none but a person of his very humane disposition would have retained him after reiterated acts of insubordination and presumption; he is of a most jealous temper and seems continually upon the watch to take offence, which he scruples not to express in rude terms. I thought it necessary to say this much in explanation, that you might know why we do not approve of Davis: I should have been very happy if he had been in all respects a proper person, for we are extremely at a loss where to find one. I have written to New Orleans on the subject, particularly to M. Lafon the author of the map of Louisiana and the View of New Orleans; tho’ I do not think that he himself is much of an Astronomer, yet he may help to discover what we want.—I have written to Colo. Freeman on the subject of boats; if none belonging to the public are of proper construction, some of those which always perish by being out of use, may be bartered away for such as will suit us. I have also written to Govr. Claiborne to know what will be the determination of the Marquis de Casa-Calvo. Should he decline giving a passport, must we not expect that our party will be stopped near the bayou pierre settlement, no great distance above Nakitosh?—I have never had the pleasure of seeing Colo. Freeman, but have been in correspondence with him and I conceive that an officer of his rank and respectability will be of considerable advantage to the progress of the expedition, particularly if he knows the use of the sextant and possesses some talents of research.

I have considered the methods you propose for ascertaining the Longitude in the event of derangement to the time-keepers. There can be no doubt as to the principle, but it seems to me that the execution will involve some new difficulties. There must be at least two good observers and a nice instrument different from the Sextant: it is at all times a Curious operation to form a meridian sufficiently correct for the purpose of being applied to the ascertainment of the Longitude, and in order to measure the moon’s distance from any meridian, we must have an instrument similar to the Astronomical Circles of Troughton, to give us the true azimuth of that planet, for the sextant would be there of no use, & this azimuth must be referred by Calculation to the pole to give us what we are in pursuit of. To find the moon’s distance from a known star when She is on the meridian of Greenwich is easily ascertained, but in order to watch & observe this distance, we must previously calculate what ought to be the moon’s apparent distance from the Star as seen from our Latitude & longitude (a very intricate calculation) & supposes the longitude nearly known, which may not be the Case: moreover the moon being on the meridian of Greenwich, will be to us always under the horizon with south declination & at all times too low for good observation: if we take the moon’s distance from a Star when the former is upon our own meridian, a good observer must be at the transit instrument to give notice of the moon’s passage, and as we have no knowledge of the apparent time to enable us to calculate the true and apparent altitudes of the moon & Star or Sun, those must both be taken by two additional observers: upon the whole the best remedy seems to be to have two good observers (three would be better) with excellent instruments & to chuse that time of the day when the Sun or Star is at a sufficient distance from the meridian, so that taking the altitude of either will give the apparent time at the moment of taking the distance between the moon and either of those: in this case it will be found always preferable to use the Sun, because it is extremely difficult for inexperienced observers (& for others) to take double altitudes of a Star with the artificial horizon on several accounts.

One other method of a very simple nature I will mention in a subsequent letter, fearing that the mail may depart too speedily to allow time at present—With the highest respect and attachment, I have the honor to be Your most Obedt. Servant

William Dunbar

DLC: Papers of Thomas Jefferson.

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