It shall be lawful for the said Judicial Committee to direct one or more new trial or new trials of any issue, either generally or upon certain points only; and in case any witness examined at a former trial of the same issue shall have died, or have, through bodily or mental disease or infirmity, become incapable to repeat his testimony, it shall be lawful for the said Committee to direct that parol evidence of the testimony of such witness shall be received.