the essential nature of the electrical processes herein first above mentioned. They are merely devices adapted to the needs of the particular situation developed primarily with a view to efficiency and economy in operation. For illustration, electricity could be generated at 6600 volts and economically transmitted from the station for a distance of a few miles, and used by a consumer whose motors operated at that voltage without any process of transformation at either end of the circuit. This would probably be done under such conditions of transmission and use. But as distances of transmission increase, transmission' at such a relatively low voltage involves either excessive size of conductors or excessive losses in transmission and the economic and practical thing to do is to step up the voltage (increase the pressure) for economy in transmission. The transformers, therefore, are merely an aid to the transfer or transmission of energy in the electrical form, or what we call electricity.”
We think, however, that the argument of complainants ignores, or at least does not accord sufficient importance to, the part played by. the transformer in the system of electrical transmission. Electricity is produced at a low voltage. For transmission over long distances it is “stepped up” by a transformer to a very high voltage; and all of the current transmitted- in interstate commerce by complainants is thus “stepped up” before transmission -in such commerce. Before it can be used by the consumer, it must be “stepped down” again to a low voltage; and all of the current received by complainants in interstate commerce is thus stepped down before being sold to or used by the consumer. And this “stepping up” or “stepping down” is not a mere change produced in the current. It is the production of a new and different current. The principle of the transformer is that the current flowing in the wires- coming into the transformer sets up an induced current in the magnetic core of the transformer, and this causes an induced current to flow in the wires going out of the transformer; the voltage depending upon the relative number of the coils of'the wires carrying the current in and those carrying the induced current out. These wires are insulated from each other, and the current going out is not the current coming in, but a new and different current, although induced by the former. Encyclopedia Britanniea (14th Ed.) article “Transformers.” The current produced by induction in the transformer results from the use of the original current but is not that current, just as eurrent produced by steam results from the use of coal but is not the-coal.
Now, so far as the production or generation tax on current is concerned, there can be no question as to its validity as applied to current transmitted in interstate commerce, we think, even though the current transmitted be conceived of as the identical current produced. The production of an article for transmission in interstate commerce is not in itself such commerce. United Leather Workers’ International Union, Local Lodge or Union No. 66 v. Herkert, 265 U. S. 457, 44 S. Ct. 623, 68 L. Ed. 1104, 33 A. L. R. 566; United Mine Workers v. Coronado Coal Co., 259 U. S. 344, 42 S. Ct. 570, 66 L. Ed. 975, 27 A. L. R. 762; Delaware L. & W. R. R. v. Yurkonis, 238 U. S. 439, 35 S. Ct. 902, 59 L. Ed. 1397. And there can be no question but that such production is taxable by the state.
In Oliver Iron Co. v. Lord, 262 U. S. 172, 43 S. Ct. 526, 529, 67 L. Ed. 929, the state of Minnesota had imposed a tax on the business of mining iron ore measured by a percentage of the value of the ore mined or produced. Substantially all of the ore when mined was loaded on cars and shipped into other states to satisfy existing contracts. In holding that the tax on production was not a burden on interstate commerce, though the ore was destined for transportation in such commerce even before it was mined, the court, speaking through Mr. Justice Van Devanter, said: “The ore does not enter interstate commerce until after the mining is done, and the tax is imposed only in respect of the mining. No discrimination against interstate commerce is involved. The tax may indirectly and incidentally affect such commerce, just as any taxation of railroad and telegraph lines does, but this is not a forbidden burden or interference.”
The same holding has been made with respect to the production tax on gas (Hope Natural Gas Co. v. Hall, 274 U. S. 284, 47 S. Ct. 639, 71 L. Ed. 1049); a tax on coal prepared and “ready for shipment or market” and destined for a market in other states (Heisler v. Thomas Colliery Co., supra); and a manufacturing tax upon goods sold in interstate commerce (American Mfg. Co. v. St. Louis, 250 U. S. 459, 39 S. Ct. 522, 63 L. Ed. 1084).
The case of Hope Gas Co. v. Hall, supra, supporting the production tax on gas, would seem to be directly in point as supporting the tax here; for the gas in that ease, just as the electricity here, was transmitted immediately