“ In taxing property so situated and used, a state may select and employ any appropriate means of reaching its actual or full value as part of a going concern-such as treating the gross receipts from its use in both intrastate and interstate commerce as an index or measure of its value-and if the means do not involve any discrimination against interstate commerce and the tax amounts to no more than what would be legitimate as an ordinary tax upon the property, valued with reference to its use, the tax is not open to attack as restraining or burdening such commerce. ”

“ A state can neither tax the act of engaging in interstate commerce nor lay a tax on gross receipts therefrom. In either case the tax would be a restraint or burden on such commerce and its imposition and invasion of the power of regulation confided to Congress by the commerce clause of the Constitution. ”

“ Minnesota, supra; St. Louis Southwestern Ry. Co. v. Arkansas, 235 U.S. 350, 367, 35 Sup. Ct. 99, 59 L. Ed. 265; United States Express Co. v. Minnesota, supra; Galveston, Harrisburg & San Antonio Ry. Co. ”