18. Tolls, according to such rates as may, from time to time, be fixed by the Magistrate of the district with the approval of the Commissioner, shall be levied on all person, animals, vehicles and other things crossing any river by a public ferry and not employed or transmitted on the public service:Provided that the Government may, from time to time, declare that any persons, animals, vehicles or other things shall be exempt from payment of such tolls.Where the tolls of a ferry have been leased under section 9, any such declaration, if made after the date of the auction, shall entitle the lessee to such abatement of the rent payable in respect of the tolls as may be fixed by the Magistrate of the district under this section.