ELECTRIC FISH SCREEN 



109 



mutator with the resistance bridge to insui-e the eHmination of all polarization effects 

 (Ivohlrausch, 1883). These temperature-resistivity data for the various streams are 

 plotted with rectangular coordinates in Figure 8. An examination of these curves 

 ?hows that there is a gi-eat variation in the resistivity of the water from various 

 streams. The Snake River water, for example, has a resistivity of 800 ohms per 

 inch cube at 60° F., while the Clearwater River water has a resistivity of 9,850 ohms, 



TErjlPERy^TUKE- KE3IST1 VITV CURVES 



Fbft 

 THE WAfER FROM VARIOUS STREAMS 



SAMfIlES IttKEN JULYIfcjTO SEPT.,l2,l92fe.. 



Fig. 9 



which is 12.3 times as great at the same temperature. This wide variation in resis- 

 tivity is due, of course, to dissolved salts taken up by the water in the stream and its 

 tributary drainage basin. An inspection of these curves shows that all of the streams 

 having low-resistivity water rise east of the Cascade Mountains and pass through 

 semiarid alkali sections. The Clearwater River rises in the Bitter Root Mountains 

 of Idaho. The other streams rise in the Cascade Mountains and are fed, in general, 



