82 THE UNITED STATES GEOLOGICAL SURVEY. [bull.227. 
section, which lias 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 stream- 
measurement data. (3) The section of instruments and supplies, which 
attends to the purchase and distribution of all the material used in the 
hydrographic branch. (<±) 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 meth- 
ods 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 func- 
tion 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 dis- 
charge for each day during the year. 
In carrying out this work, gaging stations were established at care- 
full} 7 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 
