Silas (P) was engaged as a contractor or sub in the building of the Grand Coulee Dam on the Columbia River. P brought into the state of Washington (D) machinery and supplies worth approximately $900,000. That machinery and supplies were purchased in other states. D levied upon P a use property tax of $18,423.78 (2% of the cost) and made the demand for payment. Property purchased within the state was not subject to the use tax; only property purchased outside the state was subject to that tax, but the law had provisions for making sure that double payment was not extracted. P refused to pay, and the District Court of three judges adjudged the statute void on its face. This appeal resulted.