When any poor convict shall have been confined in any prison for the space of six (6) months, for nonpayment of fine and costs only, or either of them, the sheriff of the county in which such person shall be imprisoned shall make a report thereof to any two justices of the peace for such county; if required by such justices, the said keeper shall bring such convict before them, either at the prison, or at such other convenient place thereto as they shall direct; the said justices shall proceed to inquire into the truth of said report, and if they shall be satisfied that the report is true, and the convict has not had since his conviction any estate, real or personal, with which he could have paid the sum for the nonpayment of which he was committed, they shall make a certificate thereof to the sheriff of the county, and direct him to discharge such convict from prison and the sheriff shall forthwith discharge him.