OCR Text |
Show 101 The usual field- astronomical observations will be kept up, in accordance with the elaborated scheme of survey determined upon for the prosecution of further geographical work by the officers in executive charge of the several parties. GEODETIC AND ASTRONOMICAL. The character of the observations made in this most important branch of the survey has been improved and perfected so far as consistent with the policy of covering large geographical areas during a single field-season. The problem of conducting a geographical survey over mount ainous areas by methods at once thorough and rapid presents many grave difficulties, prominent among which is the uncertainty as to the extent of the physical obstacles to be encountered. The present organization will, however, during the coming season prosecute its labors in accordance with a certain plan conditioned upon the character of the several portions of the area to be entered, and founded upon a comprehensive system of triangulation developed from bases whose extremities and azimuths are well determined, the former by astronomical methods. These series of triangles network the entire area, and in addition thereto the horizontal and vertical values of the drainage- lines of the several^ main and sub basins are determined. The progress of the geodetic survey of the character proposed is somewhat slower than by the methods employed prior to the season of 1873; but when confined to areas of the public domain that are attracting attention on account of their mineral or other resources developing, and about to be developed, where the Indian tribes are quiet, the decrease in cost because of the smaller number of persons required in each party for reasons of safety makes apparent the fact that a well- established policy as to the character of the surveys over such areas may be reached. I have reason to believe that such a course is about to be adopted, and in consequence hereafter some of the parties of the survey, at least, may annually be sent to areas not occupied by hostile Indians; while other parties may be directed to more inaccessible portions of mountain-territory, where reconnoissance- work alone is required, and where escorts will be needed. In the season of 1873, the astronomical co- ordinates of points, and the determination of meridional lines through them, were determined at Hughes', Colorado Springs, and Trindad, Col., and Fort Union, JH". Mex., all on the eastern base of the Rocky Mountain range, and a series of triangles developed from bases at these points into portions of Colorado, New Mexico, Eastern Utah, and Eastern Arizona. The labors of the season of 1874 will take up the triangulation at the points where it was left in the preceding season, for the purpose of completing it over the area extending from the latitude of Denver southward to the thirty- second parallel. The several belts will be joined to a number of points, all of which are along nearly the same meridian east of the Bocky Mountain ridge. The bases are measured by compensated steel tapes, referred to a standard, and a sufficient number of repetitions made to guarantee a small probable error. The azimuths are also carefully determined. At the extremities of the developed bases, angular measurements are taken to the most prominent points of the adjacent triangnlation- belt, which points are natural objects- usually high mountain- peaks. The extension of the triangulation is made from point to point in accordance with the plan made at the beginning of the season, and the azimuth of at least one side of every triangle determined. |