Juday—Limnological Apparatus . 
571 
pattern an arc of a large circle is laid off on the paper with 
a pencil to which a piece of cord is attached. The radius 
of this circle can be determined by the folowing formula 1 : 
x: x plus i = r : R. In this formula x = the radius of the 
portion of the paper that is cut off for the bucket of the net; 
i = the length of the bolting cloth cone; r = radius of small 
or lower end of the bolting cloth cone, while R = that at 
upper or larger end. Substituting the values given above, 
we have x : x plus 30 = 2.5 : 9, from which x = 11.5, and 
30 cm. plus 11.5 cm. = 41.5 cm., the radius of the large 
circle, or the length of the cord to be used in laying off the 
arc. 
The width of the arc in degrees may be obtained from the 
x 360 
following equation— = —2 Substituting the above values 
for x and r wehave^^? =^?and a = 78.2°. This angular 
2.5 a 
width is determined with a protractor. It is necessary, 
however, to make allowance for seams which will add fully 
2 cm. to the length and nearly that much to the width of 
the arc. The pattern should be pinned together and then 
fitted onto the canvas cone in order to make sure that it is 
the right size. 
The two sides of the arc of bolting cloth are fastened to¬ 
gether with a French seam, using silk thread and as small a 
needle as possible so that the holes around the thread will be 
very small. In sewing the bolting cloth cone to the canvas 
cone, the former is turned inside out and passed up through 
the latter, small end first, until the upper edge of the bolting 
cloth is even with the lower edge of the canvas. The two 
are sewed together and the bolting cloth cone is then turned 
right side out, so that the seam is on the outside. The 
French seam should also be on the outside of the bolting 
cloth cone. 
In making pump catches, the net is immersed in water 
up to the canvas cone and the desired amount of water is 
pumped into it. Care should be taken to prevent the 
stream of water from striking the bolting cloth directly. 
The pump is calibrated for the length of hose used and the 
quantity of water strained may be determined approxi- 
1 Apstein. Das Suesswasserplankton. Kiel, 1896. 
