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.