be used in connection with the work. The party was organized at Spokane, and at first consisted of only a packer and a cook, but was afterwards increased by the addition of a field assistant, when angle observations were begun. When occasion required, for instance in clearing the timber for a triangulation station, extra men were hired by the day. Transportation was at first by saddle and pack animals alone, but later a light spring wagon was added to the outfit.

The work was greatly retarded by smoke during the summer, which was at times so dense as to render observations impossible, and by unusually early storms in the fall. All operations were entirely suspended about October 1, the snow being so deep as to render practically impossible the ascent of the peaks used as triangulation stations. The season's work consisted in extending the triangulation from the Spokane base eastward, through a longitudinal interval of about 70 miles, to the boundary line. Fifteen stations were erected, nine of which were occupied, and one observation for azimuth was made. Another object accomplished during the field season was the identification on the ground of the Mooyie Trail monument, which had been established by the Northwestern Boundary Commission. This monument was about 8 miles west of the boundary line between Idaho and Montana, and was the nearest monument or mark of any kind on or near the international boundary that could be identified. Further reference will be made to the Mooyie Trail monument.

After the party was disbanded, Mr. Perkins proceeded to California for duty. During the winter the office work pertaining to the triangulation was done under the direction of Mr. S. S. Gannett. Three figures were adjusted by least squares, and the geodetic positions of nine points were computed. One of the stations, Divide, was found to be 6,072 feet east of the Idaho-Montana boundary line, and another station, Scotchman, was found to be 7,842 feet west of it.

Field operations were resumed in June, 1898, two parties being organized, one for the extension and completion of the necessary triangulation, the other for running the random line northward from the point determined as the intersection of the thirty-ninth meridian west from Washington with the crest of the Bitterroot Mountains.

Mr. Perkins continued the triangulation, and the line party was organized by Mr. S. S. Gannett, topographer, with Mr. D. L. Reaburn, as transit man, the latter assuming charge of the party after the work was started.

Mr. Perkins extended his work of the preceding year northward to the international boundary, occupying nine new stations and reoccupying four old ones. A high signal was erected over the Mooyie Trail monument, and this point was located. Unfortunately the character of the country was such that it was impossible to get a location by triangulation near the northern terminus of the interstate boundary line.

Mr. Gannett was instructed to carefully examine the topographic features of the country adjacent to the triangulation station Divide, in order to determine whether it was on the true summit of the Bitterroot Mountains, and then, by traverse from the Divide station, to locate the exact point on the summit from which, as the initial point, the random line should be projected northward. Observations for azimuth were obtained at Divide, the details of which will appear hereafter, and also at the end of the traverse line. This traverse was run along the divide westward through a longitudinal interval which was supposed to be 6,072 feet, but, unfortunately, owing to an error in the field computations, the location of the initial point was made 177 feet too far east. This error was discovered in the office, and in the adjustment of the random line it was entirely eliminated from the final results.

Work on the random line was commenced July 11 by the party under Mr. Reaburn, which consisted of one recorder, two rodmen, two packers, three axmen, and a cook. The region traversed was along the entire line very rough and generally covered with timber. There were few roads or open trails, and the transportation problem was a difficult one. A pack train was provided, and it was generally necessary to make long detours and to cut out trails in order to establish camps at convenient points near the line. Toward the close of the season a great deal of snow was encountered on the high ridges, the party narrowly escaping being snowed in without provisions. The survey of the random line was completed to the vicinity of the international boundary on October 31 in snow 2 feet deep.

Horizontal and vertical distances along the entire line were obtained by stadia measurements. The total rise and fall of the boundary line was about 63,000 feet, the average length of sights 350 feet, length of line about 72 miles, number of transit stations 1,051, and number of azimuth stations 17.

At the conclusion of the field season Mr. Perkins returned to the office and Mr. Reaburn was ordered to field duties elsewhere.

During the office season of 1898-99, after the triangulation had been finally computed, an adjustment of the stadia work to the triangulation was made, and tables were prepared showing the exact latitudinal and longitudinal corrections to be applied at each station of the random line. Elevations were also computed from the vertical angles for each transit station. Six sheets on mounted drawing paper, each sheet extending through a latitudinal interval of 10', were then prepared. On these sheets was drawn the boundary line in its true position, and all topographic features which had been located from the random line were indicated. Such elevations as would be useful in sketching contours were also placed on the sheets, and the sheets thus arranged were used for sketching the topography adjacent to the line.

Mr. Reaburn resumed field operations about the middle of June,

1899, the party as organized being similar to that of the preceding season. The field work which remained was to remeasure a portion of the line, place the monuments, cut out the true line, and secure additional data for the map.

The line was divided into four sections, reference to which will be made hereafter. Three of them were controlled by triangulation, but the fourth, or northernmost section, not being so controlled, it was decided to remeasure that section with the stadia, and also to make a careful comparative measurement with a steel tape. The measurement with the steel tape served not only to check this section of the line, but was also used as a basis of comparison with the stadia measurements and to determine a stadia factor, which was afterwards applied to all of the stadia work.

The measurements of the northernmost section were first made, and the northern terminal point of the line determined. The party then started southward, and the monuments were established, marked, and witnessed in accordance with the instructions. The topography was also sketched, but as the territory through which the line ran was for the most part covered with timber, it was impossible, without delaying the work beyond the limit of the available funds, to cover more than a narrow belt. This work was completed October 5, 1899, and after a short service in another locality Mr. Reaburn reported to the office in Washington for the preparation of the final notes and plats.

LATITUDE, LONGITUDE, BASE LINE, AZIMUTH, AND TRIANGULATION.

In the following pages is given a short account of the methods employed in establishing what may be termed "the control" for the boundary line.

By combining the results of the latitude, longitude, and azimuth observations with the base-line measurement, the position on the earth's surface and the length and true direction of a line were determined. Through a system of triangulation based on the line thus established the positions of points near the boundary line were computed, as well as the distances and directions between these points.

LATITUDE.

The new county court-house at Spokane having been built very close to the longitude pier of the United States Coast and Geodetic Survey of 1888, the latter could not be used as a latitude pier. A new pier was therefore built 67.4 feet east of the longitude pier, where an unobstructed view of the meridian could be obtained. (See Pl. IV.)

A Fauth combined transit and zenith telescope (No. 534) was mounted on this pier, and in August, 1896, observations for latitude, by the Talcott method, were made by Mr. S. S. Gannett. Pairs