IN GEOMETRIC TERMS

picture still more concrete, specific figures may be at-tached to specific years, the person’s income for 1930 be-ing set at $1000, that for 1931 at $1200, and so on.

We are now ready to pass to the new and radicallydifferent method of representing the real income stream.In the chart just described, horizontal distance measurestime, while vertical distance measures amount or size.The reader is now asked to shake off these conceptions.Moreover, throughout Chapters X and XI, he must beon his guard against their unconscious return. In the newcharts there is no time scale; time is not measured at all;both axes measure amount of income. The horizontalaxis represents the first year’s income, the vertical, thesecond year’s income. Thus the point in Chart 24,through its latitude and longitude, stands in a sense forboth years’ incomes combined. It represents what maybe called a given individual’s income combination, in-come stream, income position, or income situation forthe given pair of years. On Chart 24 may be shown a com-plete map of all possible income combinations, or incomepositions, so far as two years, or periods of time, are con-cerned. To represent the third year, so easily shown inChart 23 under the old method, we should need in thisnew method a third dimension. The chart would thencease to be a chart and become a three dimensionalmodel. 1

If on the map for two years, we were to draw a straightline from the origin toward the “northeast”, midway be-tween the two axes, every point on it would have itslongitude and latitude equal, that is, would represent dif-

1 The reader who wishes, after finishing this chapter, to pursue thegeometric analogy into more dimensions than the two here consideredmay do so by reading the Appendix to this Chapter.

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