The railroad from Port Huron to Flint, in Michigan, sixty miles in length, was completed on December 12, 1871. It was built by the Port Huron & Lake Michigan Railroad Company. By foreclosure of a mortgage executed by that corporation and several consolidations it became on October 31, 1900, the property of the Grand Trunk Western Railway Company and has since been a part of its system. For forty-one years after the completion of this sixty-mile road the mails were carried over it by the successive owners under the usual postal contracts and payment was made for the service quarterly at full rates. In 1912 the Postmaster General, concluding that this was a land-aided railroad within the provisions of section 13 of the Act of July 12, 1876, c. 179, 19 Stat. 78, 82 (Comp. St. § 7485), restated the account for the twelve full years during which the road had been operated by the Grand Trunk Western. Twenty per cent. of the mail pay for that period was found to be $50,359.70; and this amount he deducted from sums accruing to the company under the current mail contract. He also reduced by twenty per cent. the amount otherwise payable under the current contract for carrying the mail over this part of its system. Thus he deducted altogether $52,566.87 from the amount payable on June 30, 1913. The road had in fact been built without any aid through grant of public lands. None had passed to the Grand Trunk Western when it acquired the road; and, so far as appears, that company had no actual knowledge that any of its predecessors in title had acquired any public land because of its construction. The company insisted that the $52,566.87 thus deducted from its mail pay was withheld without warrant in law, and brought this suit in the Court of Claims to recover the amount. 53 Ct. Cl. 473. Its petition was dismissed and the case comes here on appeal. Whether the company is entitled to relief depends upon the legal effect of the following facts.