THE COMPOSITION OF THE SOIL 97 



Od^n gives a formula for effecting the calculation, but its use 

 requires some mathematical training,^ 



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 /a. Thus the percentage weight 

 of particles between i/x and 2yu, in diameter is the area bounded 

 by ordinates drawn at points i and 2 on the axis of ;ir : without 



5 10 15 20 25 30 35 



Equivalent RADii jx 



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



sensible error it is represented by the ordinate 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. 



^ 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, gi, 41-80. 



7 



