If during the service of any such sentence, it is made to appear to the court that the defendant had been convicted of one or more crimes which were not taken into account at the time of the imposition of the original sentence, the court is authorized to issue a rule directed to the defendant requiring him to show cause before the court, not less than ten days from the granting of the rule, why the former sentence should not be revoked and the defendant be sentenced as required if all of the convictions had been brought to the attention of the court at the time of the imposition of the original sentence.