232 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
read off from the manometer and controlled by the regu- 
lating cock until it remains steady at the desired point. 
When constant conditions are obtained, a steady stream 
of water will be filtering through the silk tissue into the 
reservoir and a steady overflow from the latter will be 
collected by the table trough and led off by the overflow 
tube. The water is, therefore, passing cut of the latter 
at the same speed as it passes through the area of silk 
closing the cylinder. The cover of the collecting flask 
is now quickly removed at a signal, the water runs 
steadily into the flask, and after a certain number of 
seconds have elapsed the cover is quickly replaced. The 
volume of water in the flask will be equal to the amount 
which passed through the area of silk taken during the 
number of seconds the flask was uncovered, and at the 
pressure recorded. 
Two tables giving the quantity of water filtering 
through 1 sq. centimetre of Miillergaze (various grades) 
in one second, at various pressures, were drawn up by 
Hensen, and appear in his Methodik on pages 86 and 94. 
They will be applied in the way to be subsequently shown. 
If a ring with no net attached to it were pulled 
through the water, the quantity of water passing through 
the ring would be equal to Onv, where O=area of open- 
ing, n=number of seconds the pull lasts and v=speed in 
centimetres per second. 
The speed of outflow of liquids through an opening 
can be calculated from the Torricellian theorem, and by 
the application of this Hensen concludes that— 
Ae 
S95 [1] 
where s=the pressure equivalent to the speed, v=speed 
of pull and g=acceleration of gravity =980'°9 centimetres. 
As soon as a net is hung on to the ring, the simple 
