H. S. I. SMAIL. CLXXIX. 
THE MEASUREMENT oF THE FLOW oF STREAMS 
AND ARTESIAN BORHS, AS CARRIED OUT BY 
THE PUBLIC WORKS DHPARTMENT 
oF NEW SOUTH WALKS. 
By H.S. I. SmaI, B.E., Assistant Engineer. 
[Read before the Engineering Section of the Royal Society of N. S. Wales, 
July 20, 1903.] 
In determining the flow of any stream two factors are. 
necessary, viz.:—the area of the cross section, and the 
mean velocity of the stream at that section, then Q=Av. 
There is no great difficulty in measuring the first factor A 
except in streams of enormous volume, like the Mississippi, 
but to determine v is quite another matter, chiefly for the 
reason that the velocity of any point in the cross section 
is constantly changing, even when Q and A remain constant 
and consequently the mean velocity. Many observers have 
991 
noticed the phenomenon of “‘ pulsation of moving water. 
D. F. Henry, says’ ‘‘All water in motion has an inter- 
mittent velocity increasing and decreasing according to 
some unknown law.’’ He further states, ‘‘ The lesser 
fluctuations have a duration of 30 to 60 seconds, and the 
larger ones from 5 to 10 minutes. They do not seem to be 
synchronous with the surface fluctuations and are smaller 
at the surface than at the bottom.”’ 
But the motion of water in an open channel is not simply 
a succession of impulses, on the contrary it is very complex, 
* Vide J. B. Francis, Trans. Am. Soc. C.E., Vol. viz, p. 111; Capt. 
Cunningham, Proc. Inst. C.E., Vol. uxx1., p. 7; Prof. Unwin, Proc. Inst. 
C.E., Vol. uxx1., p. 348, and many others. 
* Journ. Franklin Inst., Vol. ux11., p. 328. 
