City of Washington, June 28th 1822.
The method of determining the longitude of any place by occultations, and solar eclipses, has been, and perhaps, always will be considered among the best for that purpose. It must be acknowledged, that the process is tedious and laborious, but the accuracy of the results, when due care is taken in the operation, will amply compensate for the trouble of computing the necessary elements. In this method, particularly, we have it in our power, by a proper reduction of the latitude of the place, and of the Moon’s equatorial horizontal parallax, to find the longitude, allowing for the spheroidal form of the Earth, which, by other methods, susceptible of less accuracy, is seldom taken into view. The rough draft herewith inclosed, is intended by its author, for the use of the seminary near Charlottesville, in your neighbourhood; and I shall be gratified to learn, that the rules and process therein exhibited, have been, or may be serviceable in promoting a competent knowledge of that branch of science, with which they are connected.