Juday—Limnological Apparatus. 
575 
between them it holds the ring to which the three lines from 
the top of the net are attached. 
The top of the net is supported by three pieces of heavy 
fish line which are attached to the ring at the mouth of the 
net at one end and to a small metal ring about 2 cm. in 
diameter at the other. A short line, about half as long as 
the truncated canvas cone and strong enough to carry the 
weight of the net, is attached to the lower ring of the canvas 
cone. This line possesses a small metal ring to which the 
hauling rope is attached. The latter first passes through 
the release and a simple loop knot is tied below it before the 
rope is fastened to this metal ring. 
Then the knot in the hauling rope is adjusted so that the 
release is just far enough above the top of the net to hold it 
properly. In operating the net the plunger of the release 
is pushed down and the small metal ring attached to the 
top of the net is inserted between the wire loops on the side 
of the release. When the plunger is released the curved 
arm rises and holds the ring between the loops. The net is 
lowered carefully to the desired depth, and then hauled up 
to the point at which it is to be closed. A small brass mes¬ 
senger is sent down the line which releases the top of the 
net and permits the canvas part to fall and close the net as 
shown in Plate XXXIV, fig. 3. In order to facilitate the 
closing a small weight is attached to the ring at one side 
of the mouth of the net. 
A number of tests have shown that no contamination re¬ 
sults from lowering the net open, if due care is exercised in 
making the haul. In very rough weather, however, when 
the boat is being vigorously tossed about by the waves there 
is such a danger. Careful determination of the coefficient 
by means of a tube 3 m. long have shown that the straining 
efficiency of the net averages about 80 per cent. 
THE BIRGE CONE NET. 
This net is designed for making collections among the 
weeds along the shallow margins of lakes, or in ponds and 
pools. The cone top, (fig. 4, A), has a base of sheet copper 
2.5 cm. wide and 8 cm. in diameter, with the lower edge 
turned over so as to form a smooth rim. To the inside of 
this copper band is soldered a loop of brass wire which lies 
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