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." In another article, Dunbar gives a "Description of a singular phenomenon seen at Baton Rouge" in the spring of 1800. His fourth contribution consists in extracts from a letter dated Aug. 22, 1801, which he wrote to Jefferson, relative "to fossil bones found in Louisiana, and to Lunar Rainbows observed West of the Mississippi." In this letter, he referred to an account of "Dr. Hooks' scheme of a telegraphy, in the year 1684," which he intended to transmit to Jefferson, but found himself anticipated in that communication by a paper in the first volume of the London Philosophical Magazine. He also directs Jefferson's attention to "a certain phenomenon at sunset,"--the yellow orange color of the Eastern clouds, which ascends as the sun descends--upon which he makes certain observations and explanations, and suggestions for further investigations by philosophers.