12 Nits ZEILON, 
for the long wave-lengths assumed here, it follows that the ratio: 
is of the order of magnitude of 14). Writing further 
Y z 7 y 
p 5 A} 
Joas[ du = [© gor fo de , 
J 0 Jo 
c 
0 0 0 0 
where y is intermediate between 0 and y, we have certainly: 
9 y 
E , Ó ] 
em (Gh) em 4 l 
a 
and we are reduced to discuss: 
y 
E 
Ó dz 
[7 11 ! ll 
15) HA an 
where, if there is only slight diffusion, y is only a very small fraction 
of the “upper” depth A". 
J 
By a slightly modified reasoning, the integral k fö. y dz may be 
0 
shown to be of the same order of magnitude 15); we conclude that 
our approximation is correct, if the following conditions are satisfied: 
2 
1) The modified value = is of the order of magnitude of that 
given by Stokes” equation, 
