It consists of two parts. The first treats of the mathematical calculations and the astronomical observations made in locating the 31° of latitude and in surveying the first eighteen miles of the line of demarcation. The remainder consists of notes taken at his encampment on the Bluff, in August, 1798. These treat, for the most part, of the vegetable and animal life to be found along the line of the survey, particularly in the swamp of the Mississippi river.
He makes several interesting observations on the red and the white cypress, the former of which he says is the more valuable for strength and durability, owing to its being impregnated with resin. He also observes that the "cypress knees," as they are commonly called, never reach a height greater than the high water mark. In combating the theory of Dupratz that the cypress is propagated from its root, Dunbar says that is "invariably propagated from the seed, which is about the size of a Spanish walnut," and that he has "often observed half a dozen or more young plants produced from one apple, which often coalesce into one and sometimes the greater part perish to make room for their more fortunate brethren." He says of one species of the white oak, that "nature has so ordained that the husk embraces the acorn so firmly that they are not separated by their fall from the tree, by which means this case by its comparatively small specific gravity buoys up the acorn, and being carried along by the various current of the inundation, serves to plant distant colonies of this species." He also gives an interesting account of the cotton tree, the willow and the bamboo cane, the last of which he attempts to classify botanically. He says of the cane: "It produces a very abundant crop of grain, and that only once, for it immediately after perishes, root and branch, it is not known how many years the reed requires to arrive at this state of maturity; if we were to suppose that 25 years were its limit, it must happen that a person who has resided during that length of time in this country and who has visited many parts of it must have seen all the cane that came under his inspection once in grain, and upon the average one twenty-fifth part of all the cane in a large tract of country ought annually to yield a crop, but this is by no means the case, for I who have lived during that length of time in this country and have frequently traversed many extensive tracts of it, have never in any one year seen 1-500 part of the canes in seed of those parts that I have intimately known." He therefore concludes that it must require at least five hundred years for this plant to reach "a state of maturity to enable it to bear a crop of seed."
His description of the ornamental trees of this region is graphic and interesting. No one can read his account of the magnolia tree without being deeply impressed with the fact that he appreciated its beauty. In studying the properties of the poplar, he made a hydrometer of a thin, broad piece of plank of this material, cut across the grain. He "improved its sensibility by boiling it when very dry, in a solution of mild alkali or carbonated potash." He describes many other trees, among which are the dogwood, the redbud, the wild cherry, the horse chestnut and the sweet gum.
He records the observation of a very rare phenomenon, which he saw August 12th, when engaged upon this work. It was a rainbow that consisted of more than a semi-circle, "the vertical point" of which "did not seem more than 8 feet from the eye, although the inferior parts seemed farther removed, which produced an optical deception by giving it the appearance of an ellipsis, the transverse diameter being parallel to the horizon; this perhaps is the first natural rainbow exceeding a semi-circle which has been seen by a human eye, because to produce such an effect from the general idea formed of this phenomenon, the sun ought to be in the horizon to cause the appearance of a full semi-circle exceeded only by the parallactic angle of the elevation of the eye above the base of the rainbow, which must generally be insensible; the above effect however is easily accounted for on Newton's principles[56] from the peculiar circumstances in which I was placed."
He says that the microscope reveals in the water of this part of the country the same varieties of animalculæ which he had often examined in Europe and many new ones, which he does not remember to have seen described by any writer, and which he hopes to find leisure to describe at some future day.
After giving a brief account of some of the wild animals, reptiles, fish, and birds of this country, he concludes with lists of the "vegetable productions of the Swampy Grounds or such as are much exposed to the Annual Inundation;" the "most remarkable vegetable productions of the high lands;" and the "Trees and Plants cultivated by the Inhabitants of the Mississippi territory and by those of the adjoining Spanish Provinces."
As has been noted above, the last ten years of Dunbar's life were devoted almost entirely to scientific research. The value of his contributions to knowledge was widely recognized, and "The Forest" became familiar to the scientific world, though it was sometimes incorrectly placed in Louisiana.
Volume V. of the Transactions of the American Philosophical Society, published in Philadelphia in 1801, contains three articles from his pen, and Volume VI. of the same publication, issued eight years later, contains twelve, one of which was translated into the German and appeared in Gilbert's Annalen of Physics, vol. 31,[57] published in Leipzig in 1809. To this latter volume of the Transactions Andrew Ellicott contributed nine articles, Jose Joaquin de Ferrer, eight, Dr. Benjamin Smith Barton, five, Benj. Henry Latrobe, three, and Dr. Joseph Priestly, F. R. S., three, while to repeat Dunbar contributed twelve. This shows that Dunbar was at that time one of the most active investigators on the continent.
His contributions to the Transactions and his correspondence with Jefferson give a conception of the character and extent to his investigations. The first of these contributions was written June 30, 1800, and treats of the "Language of Signs among certain North American Indians." In this he traces certain points of analogy "between the Chinese written language and our Western language of signs." In both, says he, there are certain "roots of language in which every other word or species in a systematic sense is referred to its proper genus or root." He gives, for example, the sign for water which is a genus and shows that rain, snow, ice, hail, hoar-frost, dew, etc., are species represented by signs more or less complex, retaining always the root or genus as the basis of the compound sign. He adduces other interesting facts from this study of the subject, which cannot be given in this connection.
His Meteorological Observations for 1799, gives unmistakable evidence of his devotion to science. It shows that three times a day, each day in the year, he recorded the temperature and the barometric readings; also the direction and strength of the winds with the state of the weather, and the amount of rainfall together with remarks about the state of the vegetation from time to time. To this he adds a Recapitulation, giving the greatest, the lowest, and the mean points of the thermometer and the barometer, and the amount of rainfall for each month and then for the whole year. The Editor of the publication states in a footnote that "the society have been induced to publish this journal entire, as it is certainly the first that has been kept with so much accuracy and attention in that part of the world, and may serve as a standard with which to compare future observations."