The foregoing description of the development of a mileage tariff is applicable to only a part of the traffic. A very large volume of tonnage,--said to be not less than seventy-five per cent. in America, sixty-three per cent. in Prussia and fifty per cent. in the United Kingdom,--moves under special rates made in quite another way in response to the exigencies of commercial competition. The making of these freight rates in practice is an extremely complicated matter. No single road is independent of rates made by its rivals--rates applicable not only to competing commodities and markets, but also as affected by apparently the most remote and disconnected contingencies. Thus railway rates, as has well been said, are not a set of independent threads; they form a fabric. They are so interwoven everywhere that if one thread be shortened, it will cause a kink in the fabric that may run almost anywhere. In order to understand this it will be necessary to describe somewhat in detail the nature of competition as applied to transportation; and then to show by a few concrete illustrations, the various factors which actively enter into the determination of specific rates. Laymen and legislators do not sufficiently appreciate the extremely delicate nature of the work. Much discussion relative to railway competition seems to be based upon the assumption that it consists in the main of the competition of railway lines more or less parallel or else operating under substantially like conditions. As a matter of fact competition in transportation is to a large degree far more complex.