This ever-changing spread of rates from place to place, as between different commodities and with all possible combinations of the two, may be clearly explained by reference to the diagram at page 108, showing the gradation of charges by distance for different goods. Is it not plain that the spread between commodities at any given place is indicated by taking a vertical cross section of the diagram at that point? We have already seen that the curves, rising with increase of the distance, do so by different degrees. They cross and recross, making an intricate lace work of lines, because of the fact that while cost, in general, may increase more or less proportionately to distance, competition in its ever-varying forms, plays all sorts of pranks with the rates from point to point. The rate at any station is shown by the height of the curve on the vertical line for that place. Even, however, if the curves never crossed, but rose by evenly spraying out from the point of shipment at one end of the line, as in the case of those for the three upper classes, their relative heights would constantly change with distance. But owing to the complexities of competition the onward and upward movement of the curves for particular commodities is usually much more erratic than this. Some goods, like children, "get their growth" early. They soon attain the level of all the charge they can ever bear. Others distribute their development over a much greater distance. Sometimes, as we have observed, the coal curve will be above the wheat curve; sometimes it will be below. In other words, the vagaries of these sloping lines cause the vertical cross sections, indicative of spread, to vary from point to point all along the line. Such a thing as constancy of ratio between classes or particular goods is, in the nature of transportation things, impossible. This is a matter of fundamental importance, especially in its bearing upon the proposition, soon to be considered, of substituting a single uniform classification under government authority for the present threefold system. Moreover, it demonstrates the great commercial disturbance which might ensue from a general advance of freight rates by an indiscriminate transfer of commodities from lower to higher classes, such as was attempted in 1900. Such procedure is altogether illogical, and economically as upsetting to trade as a general "horizontal" increase or reduction of a customs tariff.