The Doctor’s next letter is addressed to Professor JAMESON, and is dated “Mourzuk, June 6, 1822.”—This letter is valuable, both as it is expressive of his affectionate and grateful remembrance of his friend and patron, and as it conveys the result of his own observations of the physical state of the country which he had visited, to one whom he well knew could duly appreciate the value of his remarks; and who, at any rate, as they had reference to Natural History, he was aware, would regard them as the best return he could make for the kindness he had previously received from the Professor. We likewise think that the letter is made up of matter sufficiently interesting to a large proportion of our readers, to excuse us for transcribing it entire. While it tends to illustrate Dr. Oudney’s character, it shows, at the same time, the devotion of his mind to the objects of his mission to Africa. “MY DEAR SIR,—I intended to have written you long ago, but my time has been so occupied by such a variety of objects, that really I could not. I am much disappointed in the climate of Fezzan, agreeably so; the temperature under cover is not much greater than in other places in the same parallel of latitude. Now it is June, and the _maximum_ of daily heat is seldom above 90 degrees, while the _minimum_ is about 80 or 78 degrees of Fah. The air is dry, as indeed several of my instruments show too well; for the ivory on several has shrunk so as to render them useless. The tube of one of the attached thermometers is bent like a bow from being confined. In another, the pressure of the glass has broken the brass clasps. The Hygrometer of Kater, generally stands at 38 or 38.5. Instruments affected by the hygrometrical state of the air, and by sound, are useless in a climate such as this. I mention sound, for instruments which act by delicate wheels are very soon deranged, and disappoint the scientific inquirer. The Barometer varies a little: there is always a change, particularly from 11 A.M. to 8 or 9 P.M. The mercury becomes depressed, in general, about the 20th part of an inch, sometimes, however, nearly a 10th. During northerly winds, the mercury rises, and in most cases, the stronger the breeze the greater the rise; from that circumstance, I have been able to predict strong breezes from that direction. On the contrary, southerly winds cause depression, and that commonly in proportion to the violence of the wind. I have not yet calculated the mean height, but it must be about 28.600 inches at the temperature of 80 Fah. Water boils at 207 Fah.; and both of these circumstances indicate a considerable elevation.