218 
Journal of Agricultural Research 
Vo. V, No. 6 
the discharge by other methods than by the use of the current meter would 
not have been practicable. Greater detail regarding the methods used 
and the experiments in general will be found in a recent publication, 1 
which discusses the results of the determinations of the value of n in 
Kutter's formula. The field work was carried on by various members 
of the Division of Irrigation Investigations, as stated in the bulletin 
referred to. 
COMPARISONS OF DIFFERENT METHODS OF MEASUREMENT OF 
VELOCITIES IN THE VERTICALS 
There are four principal methods by which the velocities in different 
verticals are determined with the current meter: The multiple-point 
method; the mean of the velocities at the 0.2- and 0.8-depth points, 
called the “two-point methodthe velocity at 0.6 depth, called the 
“single-point method”; and the vertical-integration method. 
As the main purpose of these experiments was the determination of 
the value of n, it was desired to make the discharge determinations with 
as great accuracy as possible. The multiple-point method was used, 
readings being taken usually at six points in each vertical. This was 
assumed to give the correct discharge and is the discharge used as the 
basis of the following comparisons. 
The multiple-point readings were usually taken at 0.1, 0.2, 0.4, 0.6, 
0.8, and 0.9 of the depth. The meter was held from 30 to 60 seconds 
at each point. From these measurements the discharge by the c two- 
point or the single-point method was computed and compared with the 
results of the multiple-point method. 
When the field measurements were made, in most of the experiments 
gagings were also made by the vertical-integration method. Generally 
one or two complete round trips were made with the meter at each ver¬ 
tical, the vertical movement being from 3 to 16 feet per minute. Much 
care was used to give the meter a uniform vertical velocity so that each 
portion of the section would be equally represented in the integrated 
mean. Two complete round trips were usually made, consuming from 
40 to 150 seconds, depending on the depth. The meter was generally 
moved more slowly in the shallower sections in order to give a sufficiently 
long time for the reading. 
In Table I are given the general results for all experiments. These 
are divided in five different classes of canal sections, although there is 
no marked variation for the different groups. These include nearly 100 
experiments for the two-point and the single-point methods on canals 
having discharges of from 2 to 2,600 second-feet. Only 55 experiments 
1 Scobey, F. C. The flow of water in irrigation channels. U. S. Dept. Agr. Bui. 194. 68 p., 9 fig., 20pi. 
1915. See also Scobey, F. C. Behavior of cup current meters under conditions not covered by standard 
ratings. In Jour. Agr. Research, v. 2, no. 2, p. 77-83. 1914. 
