SEA-FISILERIES LABORATORY. 233 
conditions given above no longer prevail, for the net 
introduces a resistance, under the action of which part 
of the water before the opening is pushed away to one 
side. ‘This pressure d, which resists the entrance of the 
water, has now to be found. 
It is obvious that the same quantity of water passes 
through the entrance to the net, as filters out through the 
net walls, a constant speed of pull being assumed. — It 
may be expressed shortly as—Inflow = Outflow. 
Now, if a pressure d occurs in the net opening, the 
inflow per second will no longer be Ov(s) where v denotes 
speed of pull to which by equation [1] the pressure s 
belongs and O=area of mouth opening, but will now be 
Ov (s—d) [2]. 
It assumes, however, that one important condi- 
tion has been fulfilled, namely, that the resistant 
pressure d is uniform all over the net as well as at the 
entrance, and this will be shown later to be incorrect. 
Yaking the cylindrical net first as an example, the outflow 
must be Nwid) where N=filtering area of net in sq. 
centimetres, and w=the quantity of filtrate per sq. 
centimetre at the pressure d. 
The equation now for inflow and outflow is— 
Ov(s—d) = Nwi(d) [3] 
Inflow. Outflow. 
Tn this equation O, V, s and v are known and d and 
w are dependent on one another, and have been calculated 
by the filtration experiments described above. ‘The 
following example shows how these tables and _ the 
formulae are apphed to calculate the coefficient for a 
cylindrical net. The opening has an area of 6147 sq. 
centimetres, the area of filtering silk is in the same pro- 
portion to the opening area as 1: 0°00124, the silk is 
No. 20 Millergaze, and speed of pull=53°5 cm. per 
tc 
