240 



THE AMERICAN MONTHLY 



[Aug. 



\ 



a. 



and eveutually the hour. Tlu'ii jtut the hibel to the 

 material in tiie tube. It is necessary to hiy stress on 

 this in order to avoid confusing materials found in differ- 

 ent places; we may easily expose ourselves to error if 

 collecting from different localities or from dilfercnt parts 

 of a lake. 



Another kind of rod-net, not less commonly u.sed is 

 represented in fig. 2. It differs from the other chiefly 

 by the funnel-like form of its net 

 which is not closed but open, so that 

 a wide and thick-sided cylindrical or 

 othei' glass may be tied to it with a 

 thick string (a). According to this, 

 its rod must be much stronger than 

 that of the former, because the water 

 contained in the glass vessel is of 

 considerable weight and therefore we 

 employ instead of the pretty elastic 

 c()p])er-barrels, thick bamboo sticks or 

 ])ine-poles, to which the net may be 

 fastened in the same way as formerly 

 described (b). The use of this contri- 

 vance is nearly identical with the for- 

 mer, the only difference consisting in 

 that we are not obliged to fill the 

 bowl with vvatei-. The glass untied 

 from the net, encloses already the 

 re(juired (jiiantity. But tiie frequent 

 of the gla.ss renders the whole [»ro" 

 cceding a little dall and tiresome in coni[)arison with the 

 other without glass-bottom. 



If we want to collect in the open lake, ;i boat or any 

 other water-vehicle being at our disjiosal and intending 

 only to examine the up[ter layers of the watei-, we might 

 use rod-nets; but if we have in view to collect from 

 deeper layers we are obliged to use so-called drag nets. 



tying and untyin; 



