are the three variables--N or (P-M), u or (P-2M), and the ratio N/P, all of which are given in terms of the two experimentally determined variables, so they are themselves determined by experiment. As only two of these variables are independent, it is obvious that all of them may be represented in a single twodimensional diagram, but since, in such a plot, only two of the variables are found to be at right angles with each other, it seems valuable to use rectangular axes for each pair of

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... es in order to make the relations as obvious as possible. In this way ten two-dimensional diagrams arise. Each of these may be supposed to represent a three-dimensional plot in which the third axis gives the abundance (A) of each atomic species. The ten diagrams are outlined in Table XXV.