concurring.
Braniff Airways, in challenging the power of Nebraska to lay this ad valorem tax, claims only that its planes have no taxable situs in the State. It does not claim that no fraction of the aircraft, on an apportioned basis, *603is permanently in the State. Nor does it attack this ■ apportionment formula.
My understanding of our decisions is that the power to lay an ad valorem tax turns on the permanency of the property in the State. All the property may be there or only a fraction of it. Property in transit, whether a plane discharging passengers or an automobile refueling, is not subject to an ad valorem tax. Property in transit may move so regularly and so continuously that part of it is always in the State. Then the fraction, but no more, may be taxed ad valorem.
I mention these elemental points to reserve explicitly the validity of the apportionment formula that serves as the basis of this ad valorem tax. The formula used presents substantial questions. What might be an adequate formula for a gross receipts tax might be inadequate for an ad valorem tax. Moreover, when we are faced with a due process question, we have a problem we may not delegate to Congress.
I do not think the Court takes a position contrary to what I have said. But there are passages in the opinion which blur the constitutional issues as they are blurred and confused in the interesting report of the Civil Aeronautics Board, H. R. Doc. No. 141, 79th Cong., 1st Sess., entitled Multiple Taxation of Air Commerce. Hence I have joined in the judgment of the Court but not in the opinion.