In the Head Money Cases, speaking with reference to the requirement of the federal Constitution that all duties, imposts, and excises shall be uniform throughout the United States, the court say: "The uniformity here prescribed has reference to the various localities in which the tax is intended to operate. 'It shall be uniform throughout the United .States.' Is the tax on tobacco void, because in many of the States no tobacco is raised, or manufactured? Is the tax on distilled spirits void, because a few States pay three-fourths of the revenue arising from it? The tax is uniform when it operates with the same force and effect in every place where the subject is to be found. The tax in this case, which, as far as it can be called a tax, is an excise duty on the business of bringing passengers from foreign countries into this by ocean navigation, is uniform and operates precisely alike in every port of the United States where such passengers can be landed. It is said that the statute violates the rule of uniformity and the provisions of the Constitution, that ' no preference shall be given by any regulation of commerce or revenue to the ports of one State over those of another,' because it does not apply to passengers arriving in this country by railroad or by other inland mode of conveyance. But the law applies to all ports alike, and evidently gives no preference to one over another, but is uniform in its operation in all ports of the United States. It may be added that the evil to be remedied by this legislation has no existence on our inland borders, and immigration in that quarter needed no such regulation. Perfect uniformity and perfect equality of taxation, in all the aspects in which the human mind can view it, is a baseless dream, as this court has said more than once. (State Railroad Tax Cases, 92 U. S. 575; 23 L. ed. 663.) Here there is substantial uniformity within the meaning and purpose of the Constitution."

The principles of uniformity and of reasonable classification for purposes of taxation have been especially examined by the courts with reference to inheritance tax laws.