Northern R. v. Minnesota, 278 U.S. 503, 509, 49 S.Ct. 191, 192, 73 L.Ed. 477 (1929) (We find nothing in the record to indicate that the tax under consideration, plus that already collected, exceeds 'what would be legitimate as an ordinary tax on the property valued as part of a going concern, [or is] relatively higher than the taxes on other kinds of property.'