426 REPORTS ON THE STATE OF SCIENCE, ETC. 
A current meter (propeller type), with either visible or audible revolution 
counter, is then submerged at 6 in. and at other regular depths down to a 
point of 6 in. above the river bed, in the centre of each compartment, 
readings being taken at each depth. From the plotted velocity curve an 
average velocity for the compartment is obtained. 
This velocity, in feet per minute, is multiplied by the area of the compart- 
ment, and the summation of this process for all the compartments gives 
Q for the length of river in question. ; 
At times the gradient of the river is also taken and a discharge is calculated 
and compared with the current meter observations, with a view to finding 
the appropriate coefficients for the section of river under examination. It 
may be pointed out, however, that this investigation is by no means easy of 
application on the Thames. The river is weired at average intervals of 
24 to 3 miles, and it is only when the weirs are fully drawn, or nearly so, 
that an approximately natural condition can be obtained. 
Also when the river is in full flood the water overflows the banks and 
shallow side streams flow over land and meadows which are obstructed by 
hedges, fences, buildings, etc. ‘These and many other practical difficulties 
have to be provided for, and it is largely a matter of experience as to the best 
method to be adopted under the particular conditions of each case. 
In certain cases it is found advisable to substitute rod or float readings 
for current meter observations. 
NOTE. 
The Report on Inland Water Survey was adopted at the Leicester 
Meeting of the British Association, 1933, by Sections A (Mathematical and 
Physical Sciences), E (Geography), and G (Engineering), on whose recom- 
mendation the Committee was appointed in 1932. It was felt by these 
Sections that Memorandum E and its appendices, dealing with the measure- 
ment of underground water, should be regarded as a basis for fuller 
treatment of the subject, after consultation with Section C (Geology). 
