Under the law of 1891, the Secretary of the Treasury held in 1903 (Treas. dec. no. 24742) that books printed abroad from type set or plates made within the United States could not be prohibited importation under the manufacturing clause; but the clause has been so amended in the code of 1909 that printing in this country from type set within the United States or from plates made within the country from type thus set, is required as a condition of copyright, and copyright does not hold if any of these three conditions be neglected. It follows that in the case of books so copyrighted and manufactured, any other edition must be prohibited importation. {Sidenote: Innocent importation} An English decision holds that an importer is not innocent because he does not know that an importation includes copyright matter; and the wording of our law implies the same, though an American decision held that a partner or employer is not chargeable with statute penalties for acts done without his knowledge by a partner or agent. {Sidenote: Books not claiming copyright} An indirect and significant effect of the manufacturing proviso, in the nature of a "boomerang" to American industries, is to prevent the copyrighting of works which might otherwise be partly manufactured in America. Thus the American versions of the Book of Common Prayer and of Church Hymnals no longer seek American copyright, because the thin paper editions, as on "Oxford paper," are necessarily printed abroad and could not be imported if there were copyright on other editions which might be made in America. Baedeker's "United States," though dealing exclusively with and chiefly sold in this country, is not copyrighted, being protected rather by the cost of reproducing its German-made maps and text, and by its repute as a guide book and characteristic form, which might under the doctrine of "fair use" give its American publishers some common law protection against imitators. {Sidenote: Periodicals may be imported} {Sidenote: Composite books not admitted}