
    KANSAS CITY, MEXICO & ORIENT RAILWAY CO. OF TEXAS; NORTHERN PACIFIC RAILWAY COMPANY; NEW YORK CENTRAL AND HUDSON RIVER RAILROAD COMPANY; SEABOARD AIR LINE RAILWAY COMPANY v. THE UNITED STATES.
    [53 C. Cls., 258; 251 U. S., 326.]
    Judgment was rendered in favor of the defendants in the court below. On appeal the judgment was affirmed, and the Supreme Court decided:
    The act of March 3, 1873, c. 231, 17 Stat., 558, in appropriating “ for increase of compensation for the transportation of mails on railroad routes,” directed the Postmaster General to readjust such compensation thereafter to be paid “ upon the conditions and at the rates hereinafter mentioned,” thereupon providing that the pay per mile per annum “ shall not exceed ” certain specified sums graded according to average we'ghts of mails carried per day, and further that “ the average weight * * * be acertained, in- every case, by the actual weighing of the mails for such a number of successive working days, not less than thirty by act of March 3, 1905, c. 1480, 33 Stat., 1082, 1088, increased to ninety, at such times * * * not less frequently than once in every four years, and the result * * * be stated and verified in such form and manner, as the Postmaster General may direct.”
    
      TIeM: (1) The rates specified are the maxima; and the act leaves it discretionary with the Postmaster General to fix lower rates in contracting with railroads.
    (2) The aim of the we'ghing provision is to obtain the daily average for the year; the “ working days ” and the weighing days (whether including Sundays or not), are identical; and inasmuch as the mileage of seven-day routes now greatly exceed that of six-day routes the Postmaster General, in the exercise of his discretion over rates, may adopt a general rule, to use in all cases the whole- number of days of the weighing period, Sundays included, as a divisor for obtaining the average weight, instead of omitting Sundays from the divisor, as was done when the six-day routes predominated.
    The statute prescribes that the aggregate weight for the weighing period shall be divided by the number of “ working days ”— meaning week days — included in the period; but this is directory only, so that a failure of the Postmaster General to follow this method strictly in fixing rates will not render his action void.
    The provision of the act of July 12, 1S76, c. 179, 19 Stat., 79, reducing the compensation “ ten per centum per annum from the rates fixed and allowed,” and the similar provision of the act of March 2, 1907, c. 2513, 34 Stat., 1212, refer to the statutory maximum rates, and did not impair the discretion of the Postmaster General to fix lower rates.
    So also of the like provision in the act of June 17, 1878, c. 259, 20 Stat, 142.
    The former practice of the Postmaster General of allowing the railroads the full statutory rates and average weights derived through a divisor excluding Sundays, was an exercise of his discretion in determining the pay, and not an interpretation of the statutes as requiring that the pay be so determined.
    Rejection by Congress of amendments requiring the divisor to be the number of weighing days is not an interpretation of the existing law as forbidding that method.
    Prior to the act of July 28, 1916, c. 261, 39 Stat., 429, railroad companies which had not been aided by grants, or otherwise, were free to refuse to carry the mails at rates ofliered.
    Railroad companies which receive and transport the mails and accept the compensation with knowledge that it is readjusted under a rule insisted upon by the Postmaster General, whereby the whole number of days in the weighing period, including Sundays, is used as a divisor in obtaining the average weights, can not afterwards repudiate their contracts and claim a larger compensation because the week-day divisor was not employed, as directed by the statute.
    The same considerations apply to land-grant railroads, under duty to carry the mails at the prices fixed by law, and which by statute are to receive a certain percentage of the pay authorized- in other cases; it not appearing that the Postmaster General acted arbitrarily or discriminated against them, or fixed the pay at noncompensatory amounts.
   Mr. Justice Holmes

announced the judgment of the Supreme Court January 12,1920.  