Page:Graphic methods for presenting facts (1914).djvu/108

 *ing where the temperatures are the same. From these lines it can be seen instantly that the highest velocity is at the center of the stream, as far away as possible from retarding influences. Velocities gradually grow less as the sides, the bottom, or the ice at the top are approached. Fig. 82 is an interesting piece of work and the method used in charting is justifiable, even though in this case, as in the preceding, the independent variable is plotted downward and the dependent variable is plotted horizontally.

Courtesy of Data, Chicago

Fig. 83. Relative Value of Different Coals as Compared to Anthracite Coal

The price of anthracite coal is here the "independent variable" since it is the standard or measure by which the other variable is judged. The price of anthracite coal should have been made the horizontal scale of the chart. See Fig. 84

Fig. 84. Relative Value of Different Coals as Compared to Anthracite Coal

With the arrangement shown here the curve lines for different coals appear in their correct position. Illinois coal is at the bottom instead of at the top. The heavy line here drawn for anthracite proves at a glance which fuels are better and which poorer than anthracite