Page:Graphic methods for presenting facts (1914).djvu/98

 hour, or even more frequently. The curve, therefore, was plotted on much more numerous points than are indicated by the vertical lines of the horizontal scale. Frequent observations of the gauge height and the numerous points plotted on the curve in Fig. 76 explain those fluctuations in the line of the curve which occur in the spaces between the vertical lines. Ordinarily a chart is sufficiently accurate if straight lines are drawn from point to point of the plotted data for a curve, without attempting to make a smooth, flowing line. The curve looks smooth in this illustration simply because the gauge readings were taken so frequently that the nearness of the many points made the lines joining them appear curvilinear rather than angular. Such a smooth curve would not have resulted if gauge readings had been taken only every six hours and the chart made by connecting with straight lines the points plotted for the data obtained at these longer intervals.

General Electric Review

Fig. 75. Advertising Illustration used in a Technical Magazine, with a Heavy-type Statement Proclaiming that "3000 Central Stations in the United States need a High Grade Gasoline-Electric Generating Set"

The black areas indicate the portion of the 24-hour power-house load for which the gasoline engine would be used

Another flood curve is shown in Fig. 77. The speed with which the water ran off the territory drained can be judged by the shape of the curve. It is not, however, safe to compare the shapes of the curves in Fig. 76 and Fig. 77 without noticing that in Fig. 77 we have one day represented by a space approximately the same as the space used in Fig. 76 for only six hours. If the curve of Fig. 76 were plotted on the same horizontal scale as the curve of Fig. 77, the flood would appear to be much more severe and rapid than it appears from Fig. 76.