He closes this letter by saying that politics is not a favorite subject with him, and that he would probably not introduce it again into their correspondence, unless in the view of communicating something which it might be important for Jefferson to know. However sincere may have been his intentions to abstain from writing on political matters, we find that in his next letter to Jefferson, written about four months later, he discusses at length the claim of Louisiana to West Florida, and gives a representation of the political outlook of Mississippi and of Louisiana.[38] In another letter, written three months later still, he opposes a resolution submitted to Congress "to deprive Jefferson College of thirty acres of land____and to give the same to the city of Natchez."[39]
Dunbar's greatest claim to prominence is based upon the results of his scientific investigations. His researches in this remote and then unexplored field of inquiry brought him into fellowship with the wise and learned of all countries, and gained for him a reputation wider perhaps than that of any other scientist in the history of the State. Col. Claiborne, writing in 1876, said of him that he "was not only the most learned man of his time on the Mississippi, but we have had no man his equal since."[40] Dunbar's fondness for mathematics and astronomy made him the friend and correspondent of Sir William Herschel. He also numbered among his correspondents some of the foremost scientists of his time,—Hunter, Bartram, Rittenhouse, and Rush.
During the latter part of the Spanish rule, he was appointed Surveyor General of the District of Natchez. He also served as a representative of the Spanish government in locating the 31° of North Latitude, which was established as the boundary line between the United States and the Spanish possessions east of the Mississippi. As he was never a subject of his Catholic Majesty,[41] these services were strictly professional. The relationship between him and Governor Gayoso was, however, very cordial, as is shown by their correspondence.[42] Upon one occasion,[43] Dunbar presented Gayoso with a costly sextant, which the latter needed in order to complete a course of astronomical observations upon which he was engaged. At another time[44] Gayoso had cause to thank Dunbar for the use of a "famous astronomical circle" belonging to the latter. Gayoso says of this instrument, "it surpassed my expectation,____. Every part is so delicately finished and solidly supported & so well prepared to be adjusted that it would give me courage to make an observation myself. If the instrument was not your own property I would have advised you to make a voyage to admire it. Now I think with your assistance I may with confidence and decency proceed to the demarcation of the Line as soon as I receive orders for the purpose." The sickness of Mr. Dunbar about this time was a source of great concern to Gayoso. In a third letter[45] upon this subject, written two weeks before the work upon the line began, Gayoso expressed some apprehension that, for his sake, Dunbar might imprudently expose himself. When Dunbar was at work upon the line, Gayoso wrote to him as follows: "I congratulate myself for having had the opportunity of meeting with a person so well calculated to fulfill so important a charge for which is required science with every other quality worthy of public trust; you possess them all in a degree to do honor to any country; these are my sincere sentiments."
Dunbar's services on the line of demarcation extended from May 26 to August 28, 1798, the time consumed in surveying the first eighteen miles of the boundary.[46] The preliminary observations leading to the location of the 31° were made in his private observatory on Union Hill.[47] An inundation of the Mississippi prevented the survey from beginning at the bank of the river. The water having receded by the 28th of July, Dunbar began to extend the line to the river from the point of starting, while Ellicott, the American Commissioner, continued his survey to the east.[48] Through this swamp, which was found to be 2111.42 French toises or 2 miles and 186 perches English measure, a trace sixty feet wide was cut to designate the boundary, and posts were put at intervals of a mile.
Dunbar rejoined the American Commissioners on August 20. A few days later he made the following entry in his report to the Spanish government:—"I set out on the 31st day of August bidding a final adieu to the Gentlemen of both Commissions, with whom I had spent three months in a manner highly agreeable to my own taste, and with uninterrupted harmony on my part with every gentleman of both parties, and had it not been that my family and other interests demanded my protection and superintendence, I should have with pleasure pursued this employment to its conclusion."[49] Ellicott, in his report of this survey, published in the Transactions of the American Philosophical Society, says:—"To William Dunbar, Esq., of the Mississippi Territory I feel myself under the greatest obligations for his assistance during the short time he was with us; his extensive scientific acquirements, added to a singular facility in making calculations would have reduced my labour to a mere amusement, if he had continued."[50] The same writer in his Journal, published in Philadelphia, five years after his association with Dunbar, says that he is "a gentleman whose extensive information and scientific acquirements would give him a distinguished rank in any place or in any country."[51] Since Ellicott himself was one of the foremost scientists of his time in this country[52] the value of his estimate of Dunbar cannot be questioned.
A few months after the completion of this important public survey, Daniel Clarke wrote a letter to Thomas Jefferson, in which he referred to Dunbar as "a person worthy of being consulted____on subjects relating to this Country its productions, or any philosophical Question connected with them____For Science, Probity & general information (he) is the first Character in this part of the World. His long residence in this Country, still but little known to men of letters, its Situation with respect to many Savage tribes, some of which lately inhabited the very Place where he resides & where their visages are still perceptible, the extensive Communications with remote parts presented by the Mississippi and concourse of Indians & traders, have given him many opportunities of making observations which may not have presented themselves to others and may not probably occur in future, to these may be added those he has made on the Country itself, its population, manners, Customs of the Inhabitants, the different Changes in their Government for the last 40 years, the Climate, soil & Trade which are but little known abroad."[53]
The manuscript correspondence of Thomas Jefferson, in the Archives of the Department of State at Washington shows that he acted upon this suggestion from Mr Clarke. In this collection there have been preserved fifteen letters that were written by Dunbar.
The first of these in chronological order, bears the date of July 15, 1800. It states briefly that in compliance with the request of a friend in London, Dunbar had prepared certain notes and remarks "made while upon the line of Demarcation." These he sent to Jefferson with a request that after reading he forward them to London. Jefferson, who was then President of the American Philosophical Society and a great patron of science, was so favorably impressed by these notes that instead of forwarding them as directed, he sent them to Dr. Wistar of Philadelphia with a recommendation that Dunbar be elected to membership in the Philosophical Society. On this point Jefferson wrote that he had proposed so many members at different times that he was afraid to add to the number. "Yet," says he, "Dunbar ought to be associated to us. I enclose you a letter with communications of his to Mr. Smith of London which ____will enable you to judge of his degree of science, & therefore, I leave them open for your perusal, & will pray you to seal & send them____to London." Shortly after this Dunbar was elected to membership in this, the most celebrated organization of scientists in the early history of the United States. The fact that only thirteen other Americans were added to this body during the three years from January 1st, 1799 to 1802, gives a proper estimate of the high honor conferred upon Mr. Dunbar. In writing to Dunbar, shortly after this recognition of his scientific attainments, Ellicott says: "If you do justice to your own abilities and observations, you will do credit to the society by your communications."
Before considering the character and extent of his subsequent contributions to science, the notes and remarks referred to above demand consideration. These are contained in his report of the survey to his Catholic Majesty,[54] the Spanish copy of which is in the archives at Madrid. Several years ago it was examined by Alexander Everett, who often referred to it as "a document of rare science and accuracy."[55]