such investigation, ascertain said differences and determine and proclaim the changes in classifications or increases or decreases in any rate of duty provided in this act shown by said ascertained differences in such costs of production necessary to equalize the same. Thirty days after the date of such proclamation or proclamations such changes in classification shall take effect, and such increased or decreased duties shall be levied, collected, and paid on such articles when imported fiom any foreign country into the United States or into any of its possessions (except the Philippine Islands, the Virgin Islands, and the islands of Guam and Tutuila): Provided, That the total increase or decrease of such rates of duty shall not exceed 50 per centum of the rates specified in title 1 of this act, or in any amendatory act. . . .
"(c) That in ascertaining the differences in costs of production, under the provisions of subdivisions (a) and (b) of this section, the President, in so far as he finds it practicable, shall take into consideration (1) the differences in conditions in production, including wages, costs of material, and other items in costs of production of such or similar articles in the United States and in competing foreign countries; (2) the differences in the wholesale selling prices of domestic and foreign articles in the principal markets of the United States; (3) advantages granted to a foreign producer by a foreign government, or by a person, partnership, corporation, or association in a foreign country; and (4) any other advantages or disadvantages in competition.
"Investigations to assist the President in ascertaining differences in costs of production under this section shall be made by the United States Tariff Commission, and no proclamation shall be issued under this section until such investigation shall have been made. The commission shall give reasonable public notice of its hearings and shall give reasonable opportunity to parties interested to be present, to produce evidence, and to be heard. The commission is authorized to adopt such reasonable procedure, rules, and regulations as it may deem necessary.
"The President, proceeding as hereinbefore provided for in proclaiming rates of duty, shall, when he determines that it is shown that the differences in costs of production have changed or no longer exist which led to such proclamation, accordingly as so shown, modify or terminate the same. Nothing in this section shall be construed to authorize a transfer of an article from the dutiable list to the free list or from the free list to the dutiable list, nor a change in form of duty. Whenever it is provided in any paragraph of title 1 of this act, that the duty or duties shall not exceed a specified ad valorem rate upon the articles provided for in such paragraph, no rate determined under the provision of this section upon such articles shall exceed the maximum ad valorem rate so specified."
The issue here is as to the constitutionality of section 315, upon which depends the authority for the proclamation of the President and for two of the six cents per pound duty collected from the petitioner. . . .
First. It seems clear what Congress intended by section 315. Its plan was to secure by law the imposition of customs duties on articles of imported merchandise which should equal the difference between the cost of producing in a foreign country the articles in question and laying them down for sale in the United States, and the cost of producing and selling like or similar articles in the United States, so that the duties not only secure revenue, but at the same time enable domestic producers to compete on terms of equality with foreign