I had long deemed it incumbent on the authorities of our country, to have the great western wilderness beyond the Mississippi, explored, to make known its geography, its natural productions, its general character and inhabitants. Two attempts which I had myself made formerly, before the country was ours, the one from west to east, the other from east to west, had both proved abortive. When called to the administration of the general government, I made this an object of early attention, and proposed it to Congress. They voted a sum of five thousand dollars for its execution, and I placed Captain Lewis at the head of the enterprise. No man within the range of my acquaintance, united so many of the qualifications necessary for its successful direction. But he had not received such an astronomical education as might enable him to give us the geography of the country with the precision desired. The Missouri and Columbia, which were to constitute the tract of his journey, were rivers which varied little in their progressive latitudes, but changed their longitudes rapidly and at every step. To qualify him for making these observations, so important to the value of the enterprise, I encouraged him to apply himself to this particular object, and gave him letters to Doctor Patterson and Mr. Ellicott, requesting them to instruct him in the necessary processes. Those for the longitude would of course be founded on the lunar distances. But as these require essentially the aid of a time-keeper, it occurred to me that during a journey of two, three, or four years, exposed to so many accidents as himself and the instrument would be, we might expect with certainty that it would become deranged, and in a desert country where it could not be repaired. I thought it then highly important that some means of observation should be furnished him, if any could be, which should be practicable and competent to ascertain his longitudes in that event. The equatorial occurred to myself as the most promising substitute. I observed only that Ramsden, in his explanation of its uses, and particularly that of finding the longitude at land, still required his observer to have the aid of a time-keeper. But this cannot be necessary, for the margin of the equatorial circle of this instrument being divided into time by hours, minutes, and seconds, supplies the main functions of the time-keeper, and for measuring merely the interval of the observations, is such as not to be neglected. A portable pendulum, for counting, by an assistant, would fully answer that purpose. I suggested my fears to several of our best astronomical friends, and my wishes that other processes should be furnished him, if any could be, which might guard us ultimately from disappointment. Several other methods were proposed, but all requiring the use of a time-keeper. That of the equatorial being recommended by none, and other duties refusing me time for protracted consultations, I relinquished the