aneroid barometers, the corresponding altitudes were computed by well-known methods, the agreement between the barometric and trigonometric results being close; those from the latter mode were the ones adopted, the former being employed as checks. Moreover, additional checks were sometimes obtained by measuring the angle of depression to the sea horizon.

Although the Executive Committee of the Commission appreciated the value of geodetic work of the nature described above, and although it readily saw the advantage of the application of a more accurate and detailed system of triangulation to the entire region within its sphere of study, the amount of funds available did not permit the adoption of such a scheme. When, owing to the meagre reports received from the field, the length of time devoted to the single Republic of Guatemala, and the prevalent idea that the slow rate of progress was mainly due to the triangulation, it became apparent that Corps No. 1, at this rate, would not be able to complete its field-work within the time and within the means at the disposal of the Commission, the Executive Committee was constrained to send orders to the engineer in charge of that party to discontinue his triangulation, to confine his work to a preliminary railroad survey, and to complete his task by the first of May, 1893.

TRANSIT LINE.

It is to be especially noted that in all three Corps the main line of the survey was that of a transit line, the horizontal distances being determined by the stadia method, the vertical elements deduced from angles of elevation and depression by the same means, further checked by readings of the aneroid barometer; and in the case of Corps No. 1, by more careful observations made with the mercurial barometer, a number of sets of simultaneous observations with this instrument being made at suitable points of the transit line for the purpose of determining accurately the altitudes of the points occupied, and thus serving as checks upon the results obtained in the field from the stadia method. From the many checks and the more numerous methods employed by Corps No. 1, it will be apparent that the vertical element, as determined by that party, is worthy of greater weight than in the case of the other two surveying bodies. In passing through the forests of dense tropical growth in the eastern part of Costa Rica and in the Isthmus of Panamá, Corps No. 2, in order to traverse this section within a reasonable length of time, resolved to abandon the stadia method and substitute an acoustic one, thus determining both the direction and length of the course by sound. In the heavily-wooded country from the Sabanilla Pass down to the Marañón River, in southern Ecuador and northern Perú, Corps No. 3 was obliged to improvise

methods for the purpose of expediting its progress, the region being without supplies, and quick work being necessary to avoid disaster. To this end a mountain top would be cleared and a tall, straight tree selected, stripped of its bark, furnished with a top cross-arm, measured, and then used as a stadia rod, the maximum distance thus read being as great as six miles.

In addition to the main transit and stadia line which was the backbone of the survey of Corps No. 1, it also ran compass and stadia lines, the distance and elevations being determined as heretofore by the stadia, and the directions by the magnetic needle, the transit being set at alternate stations in order to save time. These were supplemented by odometer, compass and aneroid lines, in which the horizontal element was deduced from the number of revolutions of the wheel, the directions determined by the compass, and the elevations or vertical element by the aneroid barometer. These were still further supplemented by paced lines, the pace being the standard for the linear measurement, the direction and elevation being determined as for the odometer line. In Central America, in addition to the main transit line, a number of auxiliary or side lines were run, leaving the main line at a certain point and returning to it at the same or at some other equally well-determined station; also spur lines, which do not close upon themselves, were used. In short, we find then that in Central America there was a rough triangulation covering most of the country examined, a determination of latitude by sextant observation, a determination of elevation by triangulation, cistern barometer, aneroid barometer, and stadia method, and a number of lines of varied quality intersecting the country in various directions, thus giving much data for the accurate delineation of the topography of the country, while in South America the survey was confined almost exclusively to that of a transit line.

RETURN OF THE SURVEYORS TO THE UNITED STATES.

Owing to the different character of the work performed by the several Corps, as well as the varied nature of the regions in which they operated, the rate of progress of the parties was not uniform, the Corps finishing their field-work at different dates. Corps No. 3, which ran a transit line from Quito, Ecuador, to Cuzco, a distance of 1,700 miles, returned to the United States on August 30th, 1892, and immediately set about drafting the maps and profiles intended to accompany its written report. Corps No. 2, after covering the region between Quito, Ecuador, and the Río Savegre, in Costa Rica, besides a branch to Cartagena, and surveying over 2,000 miles, was the next to arrive home, reaching its destination on June 12th, 1893. Its office-work was then taken up and in due time carried to

completion. The several members of Corps No. 1, after examining the region between the southern frontier of Mexico and the Savegre River in Costa Rica, and surveying routes which aggregate over 2,600 miles in length, returned to the United States in June and July, 1893; but, owing to the more detailed manner in which this party had conducted its work, and the greater mass of data collected, a much longer period was occupied in the reduction of its notes and the preparation of the reports and cartographic exhibits pertaining thereto. It was, consequently, the 28th of July, 1897, before the English version of the report of this Corps was finished and its last pages given to the printer.

CHAPTER VI.

CENTRAL AMERICA.

ORGANIZATION AND JOURNEY OF CORPS NO. 1 TO ITS FIELD OF OPERATIONS.

Corps No. 1, to which had been assigned the duty of studying Central America to determine its practicability for an intercontinental trunk-line, was organized in the United States by virtue of the following order:

9. The following order has been received from the War Department:

WAR DEPARTMENT,

WASHINGTON CITY, April 1, 1891.

By direction of the President the following-named officers are detailed for duty under the Intercontinental Railway Commission, appointed under a provision in the act of Congress approved July 14th, 1890, for the purpose of making 'a preliminary survey for information in respect of a continental railway recommended by the International American Conference,' and they will report in person to the Commission in this city accordingly:

CAPTAIN EDGAR Z. STEEVER, 3d Cavalry.

1ST LIEUTENANT STEPHEN M. FOOTE, 4th Artillery.

1ST LIEUTENANT LYMAN W. V. KENNON, 6th Infantry.

1ST LIEUTENANT ANDREW S. ROWAN, 9th Infantry.

2D LIEUTENANT SAMUEL REBER, 4th Cavalry.

2D LIEUTENANT CHARLES A. HEDEKIN, 3d Cavalry.

CAPTAIN WILLIAM C. SHANNON, assistant surgeon, U. S. Army, for duty as medical officer of the party to which he may be attached.