48 IOWA ACADEMY OF SCIENCE 



D=VM^') 



I 



. X 



where D=index of variability, or the amount the group as a whole varies from 

 the mean, x=amount of the deviation of any class from the mean, f=number of 

 units in the class range, or in the present calculation, unity. 



C= — . 100% 

 a 



where C=coefficient of variability. The 100% is used to get the result into 



more convenient form, and is entirely arbitrary. 



where Ea=probable error of the mean. 



E. = -. 6745 



o 



where Eo=the probable error of the index of variability. 



-^4^r\Ml 



where E<:=the probable error of the coefficient of variability. 



CONSTANTS FOR BLACK LOAM, FIRST CROP. 



n=85 Total number of specimens. 



A=71.1764 Mean average. 



5=21.7296 Index of variability. 



C=30.52% Coefficient of variability. 



Ea=1.5897 Probable error of mean. 



E5=1.1241 Probable error of index. 



Ec=2.6018 Probable error of coefficient. 



CONSTANTS FOR BLACK LOAM, SECOND CROP. 



n=133 Ea=1.7343 



A=98.1127 E5=1.2263 



5=29.6532 Ec=2.179 



C=30.22% 



CONSTANTS FOR BLACK LOAM UNDERLAID WITH GRAVEL. 



n=394 Ea=98.57 



A=101.038 E5=.6969 



5=29.0086 Ec=1.205 

 0=28.71 



