OCR Text |
Show 102 Within the main or principal triangles there is measured a series of minor triangles, covering the entire mountain- area, checked latitudinally at specified points. The checks used for the remaining detailed operations of the survey are by latitudes along the meanders, and by the connection of station- points with three or more main or prominent points within the horizon of each. The belts of triangles are further controlled by interior check- bases at distances not exceeding one hundred and fifty miles from the primary astronomical point. By these methods, forty-four main triangulation- points were occupied in New Mexico and Arizona and thirty- six in Colorado during the season of 1873. When the connection is made between the two sets, their publication will indicate the character of the results, which have so far proven very satisfactory, since the geographical position of most of the points used could not be sufficiently ascertained in advance to always insure certainty as to resulting well- conditioned triangles. A part of the topographic work of 1873, especially that in Colorado, demands a representation upon a scale of one inch to four miles, because of the intricate character of the several drainage- lines within the Rocky Mountain system. This will in no wise interfere with the regular and systematic plan proposed for the atlas of the region west of the one hundredth meridian. Since the final publication of the same, may be made upon a scale of one inch to eight miles. The remarkably fruitful results from the topographical work of the past season are a matter of much congratulation to me, since the several areas were widely distributed and the different points of departure comparatively remote. Certain of the topographical assistants, too, were inexperienced ; yet, notwithstanding all this, and the multitude of physical obstacles constantly in the path of each one of the parties, the area covered has been notably large, and almost equal to that of the season of 1871, when it was principally by reconnoissance- methods that the results were obtained. It has been alone due to the untiring vigilance of the officers in charge and the industry of the several topographical assistants that the material for the important contributions to the geography of so large a part of our western interior has been gathered. METEOROLOGICAL BRANCH. The general method of the previous seasons has been followed during that of 1873. Hourly observations have been takeu at the primary 4 astronomical stations with the cistern- barometer, psychrometer, and anemometer. As many cistern- barometers, aneroids, and psychrometers as could be used to advantage have been distributed among the different ent field- parties, and a system of observation has been so adapted to camps, triangulation, topographical, and other stations, as to insure the determination of the greatest possible number of altitudes. The record of all these observations, up to the close of the field- season of 1873, has been transcribed upon computation- sheets, corrected and reduced, and the computation of altitudes is going forward. It is proposed to group these altitudes, in accordauce with the main topographical features of the couutry, in tables, which will appear in volume 3 of the series of publications. The contents of this volume will be- 1st. A synopsis of the general plan for meteorological observations, the methods of reduction aud computation, and the application of the results. |