"Fourth. When such books form parts of libraries or collections purchased en bloc for the use of societies, institutions, or libraries designated in the foregoing paragraph, or form parts of the libraries or personal baggage belonging to persons or families arriving from foreign countries and are not intended for sale: _Provided_, That copies imported as above may not lawfully be used in any way to violate the rights of the proprietor of the American copyright or annul or limit the copyright protection secured by this Act, and such unlawful use shall be deemed an infringement of copyright. {Sidenote: Seizure} {Sidenote: Return of importations} "(Sec. 32.) That any and all articles prohibited importation by this Act which are brought into the United States from any foreign country (except in the mails) shall be seized and forfeited by like proceedings as those provided by law for the seizure and condemnation of property imported into the United States in violation of the customs revenue laws. Such articles when forfeited shall be destroyed in such manner as the Secretary of the Treasury or the court, as the case may be, shall direct: _Provided, however_, That all copies of authorized editions of copyright books imported in the mails or otherwise in violation of the provisions of this Act may be exported and returned to the country of export whenever it is shown to the satisfaction of the Secretary of the Treasury, in a written application, that such importation does not involve willful negligence or fraud. {Sidenote: Rules against unlawful importation} "(Sec. 33.) That the Secretary of the Treasury and the Postmaster-General are hereby empowered and required to make and enforce such joint rules and regulations as shall prevent the importation into the United States in the mails of articles prohibited importation by this Act, and may require notice to be given to the Treasury Department or Post Office Department, as the case may be, by copyright proprietors or injured parties, of the actual or contemplated importation of articles prohibited importation by this Act, and which infringe the rights of such copyright proprietors or injured parties."