13. Judge may summon witnesses to attend at certain time and place. Examination of witnesses about to leave Calcutta.-- It shall be lawful for the Judge of the said Court, at the instance of the prosecutor, or of the party accused, or of his own motion, by writing under his hand, to summon any person to attend as a witness at a time and place to be specified in the summons, for the purpose of being examined at any trial before the said Court; or if such person shall be about to depart from Calcutta, so as to be unable to attend at such trial without serious inconvenience, then to be examined before the Judge of the said Court before the day fixed for the trial: Provided always that due notice of the time and place of such examination shall be given to the accused party; provided also that such witness may nevertheless be examined at the trial if he shall be able to attend thereat in which case his previous examination may also be read at the trial.