The term for which copyright shall subsist shall, except as otherwise expressly provided by this Act, be the life of the author and a period Of fifty years after his death:
Provided, that at any time after the expiration of twenty-five years, or in the case of a work in which copyright subsists at the passing of this Act thirty years, from the death of the author of a published work, copyright in the work shall not be deemed to be infringed by the reproduction of the work for sale if the person reproducing the work proves that he has given the prescribed notice in writing of his intention to reproduce the work, and that he has paid in the prescribed manner to, or for the benefit of, the owner of the copyright royalties in respect of all copies of the work sold by him calculated at the rate of ten per cent. on the price at which he publishes the work ; and, for the purposes of this proviso, the Board of Trade may make regulations prescribing the mode in which notices are to be given, and the particulars to be given in such notices, and the mode, time, and frequency of the payment of royalties, including (if they think fit) regulations requiring payment in advance or otherwise securing the payment of royalties.