32 Instructions to Field Parties. 



either of the water or of the saturated soil, by sticking the bulb of 

 a thermometer in and leaving it for some moments. The resist- 

 ance is then corrected for this temperature according to the direc- 

 tions given below, n 



Reduction of resistances to a temperature of 60° F. — A single illus- 

 tration will serve to show the way the following table is used in 

 the reduction of electrical resistances to a uniform temperature of 

 60° F. : Suppose the observed resistance of the soil is 2,585 ohms 

 at a temperature of 50.5°. In the table, at the temperature of 

 50.5°, as indicated on the left-hand side, we find that at that 

 temperature 2,000 ohms is equal to 1,748 ohms at 60°; 5,000 ohms 

 is equal to 4,370 ohms at 60°; hence 500 ohms would be equal 

 to 437 ohms. Similarly, 80 ohms would be one-hundredth of 

 the value given for 8,000 ohms at 50.5° in the table, therefore 

 equal to about 70 ohms at 60°, while the 5 ohms would be equal 

 to about 4 ohms. These separate values are added together thus: 



2,000 1,748 



500 437 



80 70 



5 4 



2, 585 ohms at50.5°=2, 259 ohms at 60' 



