224 
IOWA ACADEMY OF SCIENCE Voi.. XXVII, 1920 
Fig. 46 
A family of curves is plotted, as in the figure, with ordinate 
and abcissa Log aD and Log ct respectively, with “b” a parameter. 
The experimental curve is plotted upon tracing paper with Log D 
and Log t as ordinate and abcissa respectively. The tracing paper 
curve is now shifted over the family of curves, — preserving 
parallelism of axes, — until it coincides with a part of one of the 
family. The “b’’ is determined by the particular curve of the 
family choseh for coincidences, and the “a” and the “c” are given 
by the intercepts of the axes of the experimental curve upon the 
axes of the family of curves. 
Physical Laboratory, 
Th^ State University oe Iowa. 
