THE COMPOSITION OF THE SOIL 



97 



Oden gives a formula for effecting the calculation, but its use 

 requires some mathematical training. 1 



The type of curve finally obtained is shown in Fig. 1 5. 

 This is a mass distribution curve : not a frequency curve. 

 On the horizontal axis are plotted successive values of the 

 radii. The axis of y represents a complex function which 

 gives the percentage weight of particles comprised between 

 successive integral values of //,. Thus the percentage weight 

 of particles between 1/j, and 2fj, in diameter is the area bounded 

 by ordinates drawn at points I and 2 on the axis of x : without 



i6 

 O 



LJi2 







LU 



LJ 



O 

 QC 

 LJ 



Q- 



30 



35 



5 10 15 20 25 



EQUIVALENT RADII /x 



FIG. 15. Mass distribution curve obtained by Odin's method of soil analysis. 



sensible error it is represented by the ordihate drawn from the 

 point i -5. 



It is improbable that this could ever become a working 

 analytical method ; but as a method for investigation it sur- 

 passes any other at present available, because for the first' 

 time it affords the possibility of representing the soil fractions 

 by a distribution curve of the type familiar to physicists and 

 mathematicians. 



1 A full description of the method and the mode of calculating the results 

 will be given in B. A. Keen's monograph in this series. A simpler method is 

 described by O. Wiegner, Landw. Versuchs-Stat., 1918, 91, 41-80. 



7 



