782 STATE BOARD OF AGRICULTURE. 



the diurnal-nocturnal amplitude of oscillation of temperature decreases 

 in geometric progression as tlie depth increases in arithmetric pro- 

 gression. The extraordinary closeness with which the actual fluctuation 

 follows this law is shown by Table 75, which contains the observed and 

 calculated fluctuation of the five different types of soil at four different 

 depths. The observed amplitudes were obtained by taking records of the 

 temperature every 20 minutes until the absolute maximum and minimum 

 were attained at all different depths. The calculated values were se- 

 cured by dividing the lowest observed fluctuation by the one preceding 

 and then multiplying the other observed values by the ratio or constant 

 thus obtained. 



