The primary purpose and function of the postal service being the transportation of government and letter mail, second, third, and fourth class matter are not strictly chargeable with that proportion of the total cost of the service which would be equivalent to their proportion of total weight or volume, but these secondary classes, on the contrary, are chargeable only with that fraction of total cost which would remain after deducting all expenses of installation and general management involved in the maintenance of a complete postal service for government and letter mail. This method of computation should be applied not only in respect of the expenses of administration and handling, but especially in respect of the expense of railway mail transportation, in which, by reason of the sliding scale of payment, the additional burden of second-class matter entailed but _an infinitesimal additional cost_. As an illustration of this point, attention was drawn to the statement of Dr. Henry C. Adams, in his report to the commission of 1898 (p. 404), that _if the volume of mail had been decreased so that the ton-mileage had been 169,809,000 instead of 272,000,000, the railway mail pay would have been practically the same_. In other words, the argument is that the true cost of second-class matter is merely that part of total cost which _would be saved if second-class matter were now eliminated_. The foregoing is from page 9 of the commission’s report. On the same page of the report it gives a summary of another set of reasons presented by the publishers in their argument in support of their contention that the mail rate on second-class matter should be low: That second-class matter, by reason of the fact that it is handled largely in bulk in full sacks already routed and separated and requires little or no handling by the railway mail service or the force at the office of mailing and of delivery, is in fact the _least expensive class of matter_. With respect to the proportion so routed and separated, it was variously estimated by the publishers as from _70 to 93_ per cent of the total weight. The assistant postmaster at New York fixed the percentage for his office at _67 per cent_, and the assistant postmaster at Chicago estimated it, for the country at large, to be between 50 and 60 per cent.