Product of ton-mileage of Ton mileage Ton-mile rates of 1907 and ton-mile Group of 1907. 1897 in mills. rates of 1897. I 6,511,166,971 12.02 $ 78,264,226.99 II 63,455,243,659 6.75 428,322,894.70 III 47,994,909,002 6.05 290,369,199.46 IV 11,418,243,141 6.48 73,990,215.55 V 17,397,321,360 8.64 150,312,856.55 VI 44,318,734,155 8.55 378,925,177.03 VII 9,300,234,849 11.48 106,766,696.07 VIII 17,406,430,971 10.79 187,815,390.18 IX 7,546,655,555 10.40 78,485,217.77 X 11,252,450,440 12.75 143,468,743.11 --------------- ----- ----------------- United States 236,601,390,103 -- $1,916,720,617.41 By dividing the aggregate of the products in the last column of the foregoing by the total ton-mileage shown in the second column, an average is obtained which represents the ton-mile rate that would have resulted in 1907 had the traffic of each group in that year moved in precisely the same volume in which it actually moved and had the average rates in each group been exactly the same as they were in 1897. This shows that, under the conditions assumed, the average ton-mile rate for the whole country would have been 8.10 mills or 0.12 mill higher than in 1897. This advance of 1.50 per cent. would have been wholly due to the more rapid growth of traffic in the regions of normally higher rates. The chief significance of so small a change in so long a period is, really, to indicate that the ton-mile unit, so far from being of rapidly changing character, is actually, at least as far as it might be assumed to be affected by changes in the location of traffic movement, a fairly stable unit and thus an excellent measure of the rise or fall in rates. Whether the same conclusion is to be derived from a study of the changes in the proportion of the total movement made up of commodities of different grades and naturally taking different rates is now to be made the subject of inquiry. Publication of the classified statistics of tonnage necessary for such an inquiry was begun by the Interstate Commerce Commission with the report for the year 1899. Consequently it is not practicable to extend the inquiry to a period prior to that year. The following statement shows the number of tons of freight of each of the classes of commodities named which were received by the railways for transportation in 1899, 1903 and 1907 and the proportion of the tonnage in each class to the total number of tons carried: