With the exception of limited studies on Potomac River at Chain Bridge, D. C., until the fall of 1894 the work of the hydrographic division had been confined to those districts where irrigation investigations were being carried on. With the expansion incident to the increased appropriation of that year it became necessary to reorganize the division on a more permanent basis. To employ salaried hydrographers to carry on all the field work was evidently impracticable in view of the smallness of the appropriation. The difficulty was overcome by securing gratuitous or inexpensive cooperation from men who had not only a strong personal interest in and inclination toward investigations of this character, but also some permanent occupation or position, so that they were not dependent upon remuneration from stream-gaging funds. Assistance of this kind was given by professors of geology or of hydraulic engineering, and by local and civil engineers who had practical acquaintance with the difficulties and methods of water measurements and with the behavior of streams and underground sources of supply in their respective localities. For convenience in administration the States and Territories were grouped. into hydrographic districts, each under the care of a division hydrographer who looked after the work done by the men in his section. The data collected in each section were transmitted to the Washingtor office, where the material was prepared for publication.

Although a large amount of data was collected and much good work was done by the cooperative system, it was found to have the disadvantage that the aids were occupied with other duties at the times when it was most desirable that measurements should be made. Therefore, as the appropriations have warranted, the temporary employees have received permanent appointments or have been replaced by men who are able to devote their whole time to the work.

With the increasing appropriations the stream-measurement work has been extended from year to year, so that at present measurements have been or are being made on practically all the principal rivers in the United States; and in connection with these records of flow other hydrographic data, such as river profiles, extent of and damage done by floods, water-power data, etc., have been collected. During last year (1903) regular stations were maintained at about 500 points, distributed so as to cover the greatest needs of the various States and Territories. Figs. 2 and 3 show the locations of these stations.

Under the present organization of the division of hydrography the work is divided between the field and the Washington office. In the field every effort is put forth to collect as much information as possible. This is transmitted through the local offices, where it is examined, to the Washington office. The plan of dividing the country into hydrographic districts has been continued, and the present division is as follows: New England, New York, northern Atlantic States, southern

Atlantic States, Mississippi Valley States, Texas, and the Western or reclamation States.

The work in the Western or reclamation States is carried on in connection with investigations by the resident engineers of the reclama

tion service. There is a general inspector of field work, who, with each resident hydrographer, visits at intervals the various stations in his district. At the times of these visits the equipment is examined, measurements are made, and such suggestions and recommendations are given as will bring the work in each district to a uniform standard.

The Washington office looks after the general administration of the work, cares for the supplies and accounts, receives the original data as collected by the resident hydrographers, and prepares the material for publication. The Washington office comprises the following four

sections: (1) The executive office, which looks after appointments, assignments to duty, general correspondence, approval of accounts, bookkeeping, and other matters in connection with the administration of the work. All material passes through and is inspected by this office before it is submitted to the hydrographer. (2) The computing

section, which has charge of the files that contain all original records. It inspects the data that come into the office from the field, makes the computations necessary for preparing the material for publication, and compiles the annual report, which contains the data collected. To this section all requests are referred for information in regard to streammeasurement data. (3) The section of instruments and supplies, which attends to the purchase and distribution of all the material used in the hydrographic branch. (4) The publicity section, which reviews all the data and correspondence that come into the office and extracts such portions as may be of immediate interest to the public at large. Visitors to the office are received by this section and directed where to obtain such information as they may desire.

The stream-measurement work done prior to 1888 was confined to particular localities and to short periods of time. Such results were of limited value, and it was necessary for the Survey to devise methods whereby data could be collected, as it were, by wholesale. The entire country had to be studied, and it was essential that observations should be extended over a considerable period of time, in order that both the total flow and the seasonal distribution could be determined. It was held by those organizing the service that, in work involving so many disturbing factors, observations of a fair degree of accuracy, covering a long period, were of much more value than more accurate observations covering short periods.

In order to fulfill the required conditions it was found necessary to measure and record from time to time two variable quantities. The first of these was the mean daily height of the river, referred to some arbitrary datum; the second, the discharges to correspond to these heights. With these data, assuming that the discharge is a function of the gage height, and that like gage heights will have like discharges, it is possible to construct a rating table which will give the discharge for each stage of the river. From this table, with the daily gage heights, there may be compiled a table showing the discharge for each day during the year.

In carrying out this work, gaging stations were established at carefully selected points on the various streams. In the East results are wanted mainly for water-supply and power purposes; in the central part of the United States, for water-supply and sanitary purposes; and in the West, for irrigation. Some stations in each section of the country are needed for general statistical purposes, and all the records are valuable in studying flood conditions. Therefore, the endeavor is made so to locate the stations that it is possible to procure the requisite data with the proper degree of accuracy and at reasonable cost. Data for low and ordinary stages are more valuable for power purposes than are the data for higher stages, hence low-water conditions govern in selecting stations for this purpose. Where the data are to be used