"For a few years, however, prior to 1873 the distribution of the mails in transitu had been practiced to a sufficient extent to satisfy the Post Office Department and Congress that it was a desirable innovation and a branch of the postal service that should be very much enlarged. But it was recognized that if the railroads were not only to transport the mail itself, but also to supply, equip, and haul post offices for the distribution of the mails, the compensation upon weight basis that had obtained up to that time was not entirely adequate and just, and therefore the law of 1873, as already indicated, contained a provision allowing additional compensation for railway post office cars. At first these cars were mostly not exceeding 40 or 45 feet in length and of light construction, similar to baggage and express cars. "From the policy of the Department, however, of constantly demanding better and better facilities from the railroads and the introduction of every improvement that could be discovered, it has come to pass that, today, the railroad post office cars, with the exception of a few obsolete ones that are being discontinued as rapidly as practicable, are elaborate structures, weighing between 90,000 and 100,000 pounds; built as strongly and fitted up, so far as suitable to the purpose for which it is intended, as expensively as the best Pullman and parlor cars; costing from $5,200 to $6,500; maintained at a cost of $2,000 per year; traveling on an average of 100,000 miles per annum; provided with the very best appliances for light, heat, water, and other comforts and conveniences; placed in position for the use of the postal authorities from two and a half to seven hours before the departure of the train upon which they are to be hauled, and owing to the small space allowed in them for the actual transportation of the mails, accompanied on the denser lines by storage cars for which no additional compensation is paid by the Government and on the less dense lines the larger bulk of mails is carried in the baggage cars without additional compensation for the car. "These cars are constructed and fitted up by the railroads in accordance with plans and specifications furnished by the Department, and the amount of mail transported therein is determined exclusively by the postal authorities. From these two facts it results that the railroad must haul 100,000 pounds of car when the weight of the mail actually carried therein is only from 3,500 to 5,000 pounds--often very much less, and occasionally somewhat more.