provided further, and as a condition of extending the copyright control to such mechanical reproductions, Compulsory
licenseThat whenever the owner of a musical copyright has used or permitted or knowingly acquiesced in the use of the copyrighted work upon the parts of instruments serving to reproduce mechanically the musical work, any other person may make similar use of the copyrighted work upon the payment to the copyright proprietor of a royalty of two cents on each such part manufactured, to be paid by the manufacturer thereof; and the copyright proprietor may require, and if so the manufacturer shall furnish, a report under oath on the twentieth day of each month on the number of parts of instruments manufactured during the previous month serving to reproduce mechanically said musical work, and royalties shall be due on the parts manufactured during any month upon the twentieth of the next succeeding month. The payment of the royalty provided for by this section shall free the articles or devices for which such royalty has been paid from further contribution to the copyright except in case of public performance for profit: And provided further, That it shall be the duty of the copyright owner, if he uses the musical composition himself for the manufacture of parts of instruments serving to reproduce mechanically the musical work, or licenses others to do so, to file notice thereof, accompanied by a recording fee, in the copyright office, and any failure to file such notice shall be a complete defense to any suit, action, or proceeding for any infringement of such copyright.
Damages"In case of the failure of such manufacturer to pay to the copyright proprietor within thirty days after demand in writing the full sum of royalties due at said' rate at the date of such demand the court may award taxable costs to the plaintiff and a reasonable
