184 
A still more accurate determination of the total amount of 
solids in suspension in the river, both silt and plankton, is 
afforded by the catches made by the Berkefeld army filter, 
data concerning which will be found in Table XV. This filter 
removes all of the suspended solids and permits their complete 
removal from its surface, but adds a small portion of its own 
substance to the catch. After the first few catches with this 
filter the wear becomes somewhat uniform and is thus dis- 
tributed. On computing the loss from the filtering sur- 
face by wear, and quadrupling this volume to allow for its less 
compact condition, we find that it constitutes less than five 
per cent. of the catches washed from its surface. The true 
amount of solids is thus about five per cent. less than the 
figures cited in the tables and in the following discussion. 
The amount of water strained in making these catches was 
usually 5 liters, while the tables give the computed amount 
per cubic meter. 
The amount of solids was measured by our usual method 
of measuring plankton, that is, by condensation in a centrifuge. 
In this treatment it usually attains the consistency of soft mud. 
For the river the amount ranges from 148 cu. cm. (per cubic 
meter), in declining water under the ice in December, to 5,416 cu. 
cm., in the incipient stages of the winter flood of February 28, 
1899. The average amount of the weekly catches for 1898 is 
592.2 cu.cm. per cubic meter, which for an average flow of 
24,600 cubic feet of water per second (see page 132) means a 
discharge of 14.57 cu. ft. of solids per second, or, 459,794,232 
cubic feet (1,301,990 cubic meters) per year, or 16,472 cu. ft. 
(46.64 cu. meters) per square mile of the catchment-basin of 
the river. 
The average amount, per cubic meter of water, of solids 
taken at fortnightly intervals in 1898 in Quiver Lake was only 
378 cu. cm., a fair index of the greater clearness of its waters. 
In Thompson’s Lake similar collections average 557 cu. cm., in- 
dicating waters somewhat clearer than the river. In Phelps 
Lake the average amount is large, 1,572 cu. cm., due in no small 
