In the upper portion of the illustration lines are drawn through all those points in the stream cross-section which have the same velocities. The lines are similar to the well-known isothermal lines on a weather map show-

GRAPHIC METHODS

ing where the temperatures are the same. From these hnes 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.

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AELATIve VALUE IN DOLLARS

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Counesy 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. 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.

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