United States Postal Laws and Regulations, Section 1164, provide that the average weight of the mails used in fixing rates shall be established by the actual weighing of the mails for a period of not less than thirty days and "_not less frequently_ than one in every four years." The construction placed upon this by the Department has been the one which reduced to the minimum the pay which the railroads receive for services rendered. If mail traffic were stationary, weighing every four years would not matter much, but the increase of mail matter throughout the United States has been very great, and, because of the policy of the Department, to weigh the mails not more frequently than every four years, heavy losses have resulted through the railroads having to haul tonnage for three successive years following each weighing for which they receive no pay. As a result of this policy of quadrennial weighings, the roads in Interstate Commerce Groups 7, 8, 9 and 10 (including the territory west of the Missouri river and the Mississippi below St. Louis) between 1878 and 1905 suffered a loss of $19,200,000, or 12 per cent. of the aggregate railway mail pay, compared with what they should have received if the mails had been weighed annually. In other words, this loss is equivalent to a reduction in the rate received per ton mile in these groups of states of 12 per cent. The loss to roads in the western part of the United States is most striking, due as it is to the rapid growth of that section. The same reduction, though to a slightly less degree, obtains in other parts of the United States. COMPARATIVE RETURNS TO THE RAILROADS FROM CONDUCTING MAIL. PASSENGER AND FREIGHT SERVICE IN THE UNITED STATES. In order to make a fair comparison of operating results from different classes of traffic, it is necessary to consider them under substantially similar conditions. The best measure of railroad service is work done, or weight multiplied by distance carried; in other words, the ton mileage. A comparison of services differing so widely as the mail, passenger and freight on the basis of ton mileage of such business is, however, unfair, because in the two former an excessive proportion of dead weight must be transported for each ton of paying load, whilst with freight traffic the proportion of dead weight is small. The hauling power of a locomotive is measured not by revenue ton miles, but by ton miles of gross weight, it making little difference to the locomotive as to what this gross ton mileage is composed of, the gross tonnage and the speed at which it must be moved being the factors that consume the energy of the locomotive.