there.[729] Recently, however, this long standing rule has been amended by the addition to it of the apportionment rule as developed in the Pullman case. This occurred in Ott _v._ Mississippi Barge Line Co.,[730] decided in 1949, in which the Court sustained Louisiana in levying an _ad valorem_ tax on vessels owned by an interstate carrier and used within the State, the assessment for the tax being based on the ratio between the number of miles of the carrier's lines within the State and its total mileage. Airplanes When, however, it was confronted by an attempt on the part of the State of Minnesota to impose a personal property tax on the entire air fleet owned and operated by a company in interstate commerce although only a part of it was in the State on tax day, the Court found itself unable to recruit a majority for any of the above formulas.[731] Pointing to the fact that the company was a Minnesota corporation and that its principal place of business was located in the State, Justice Frankfurter for himself and three others wished to stress the prerogatives of the State of domicile.[732] Justice Black, concurring in this view, added the caveat that the taxing rights of other States should not be foreclosed and made reference to his "leave it to Congress" notion.[733] Justice Jackson, after speaking lightly of the apportionment theory,[734] joined the affirming brethren on the ground that the record seemed "to establish Minnesota as a 'home port' within the meaning of the old and somewhat neglected but to me wise authorities cited," to wit, the Hays case and those decided by analogy to it.[735] Four Justices, speaking by Chief Justice Stone dissented, urging the Pullman Case[736] as an applicable model and the fact that "the rationale found necessary to support the present tax leaves other States free to impose comparable taxes on the same property."[737] Evidently in this area of Constitutional Law the Court is still much at sea or better perhaps, "up in the air." Motor Vehicles