
    ALABAMA GREAT SOUTHERN RAILROAD COMPANY v. THE UNITED STATES.
    (25 C. Cls. R., 30; 142 U. S. R., 615.)
    
      On the defendants’ Appeal.
    
    The claimants own and operate a railroad line, portions of which, are “ land-grant roads.” Under the act 12th July, 1876, the Post-Office and Treasury Departments allow full compensation for service dn the unaided portions of the line. A subsequent Postmaster-General restricts compensation over the whole line to “land-grant rates;” and also deducts from the payments made by his predecessors on the unaided portions.
    The court below decides:
    Congress can not compel a non-land-grant road to carry the mail, but can restrict the compensation to land-grant rates.
    The Act 12th July, 1876 (19 Stat. L., p. 82), provides that if “ a railroad was constructed in whole or in part hy a land grant,” it shall receive only 80 per cent of the compensation allowed to unaided roads. The language being ambiguous, the court willnot disturb the contemporaneous construction of the Post-Office and Treasury Departments, that where a road had been aided in whole or in part the reduction of compensation will be in whole or in part.
    Where the responsible officers of the Government give a construction to a statute, upon the faith of which a contractor renders a service and receives his pay, the Government can not subsequently open the transaction and recover back the money upon a different interpretation of the law.
    
      The Band-grant Acts 3d June, 1856, 11th August, 1856 (11 Stat. L., pp. 17, 30), provide that “the mail shall he transported over said roads at such price as Congress may by law direct.” But a grant to Alabama “to aid in the construction of the following roads in said State” can not be construed to extend the conditions of the grant to an unaided portion of the road in another State.
    A continuous line of road made up of land-grant and non-land-grant portions, though owned and operated by one company, is nevertheless, when considered as a mail-carrier, two distinct roads operated by different parties.
    A limitation set by Congress upon the price to be paid for-mail transportation will bind the Postmaster-General not to incur a greater liability, and be notice to the carrier.
    The decision of the court below is affirmed on the same grounds.
   Mr. Justice Brown

delivered the opinion of the Supreme Court, January 18, 1892.  