1856.] Report on the Magnetic Survey, 29 



stream can be taken into consideration in estimating the discharge 

 of water, the Eastern part being formed by sand banks or still 

 water. 



The area of the section between the distance of 665 meters and 

 1420 meters from the left shore contains, as found by projecting it 

 on paper where 5 square millimeters are equal to 1 meter square of 

 the natural size, 



8044 square meters. 



This must be multiplied by the mean velocity. 



The mean velocity lies, as an inspection of the table of velocities 

 shows, between 



1.0 and 1.2 meters per second 

 it can be determined more accurately by the formula 



m = s — \/s + 0.5,* 

 where m is the mean velocity, s the surface velocity in English inches 

 per second, from which the meters are got by multiplying the result 

 by .0254. 



The surface velocity being 1.30, 1.42, 1.15 meters or 1.29 meters 

 on an average, the resulting mean velocity is 1.12 meters a second. 



This multiplied by 8044 the number of square meters as mention- 

 ed above gives as the discharge of water in 1 second of time. 



9010 cubic meters = 318200 cubic English ft. 



To get an approximate idea of the discharge during the greatest 

 height of the water the following considerations may guide us. 



The velocity in the main stream of the Brahmaputra during the 

 height of the water after the rains, approximately ascertained from 

 the rate of boats at the time of low and of high water is at least f 

 of what it is at present, a velocity, sometimes even exceeded in times 

 of rapid rises of the river. 



The increase of the section of the main stream between 665 and 

 1420 meters from the left shore is, as shown by the section 6750, 

 square meters. 



These multiplied by 1.68 gives an increase of water 



= 11340 cubic meters. 



* The bottom velocity " b," expressed by the formula b =2m — s becomes 

 0.95 meters per second. 



