Note 734 — ARTICLE I (continued 4)

"The apportionment theory is a mongrel one, a cross between desire not to interfere with State taxation and desire at the same time not utterly to crush out interstate commerce. It is a practical, but rather illogical, device to prevent duplication of tax burdens on vehicles in transit. It is established in our decisions and has been found more or less workable with more or less arbitrary formulae of apportionment. Nothing either in theory or in practice commends it for transfer to air commerce."—Ibid. 306.