Whenever the Chief Justice of the Supreme Court of Alabama shall, because of illness or otherwise, be disabled from actively performing his duties as chief justice or those ex officio duties imposed upon him by law or shall be absent from the court for a period of 30 days or longer, then, in either event, the duties so imposed upon him shall be performed by the available associate justice of the Supreme Court in order of seniority based upon continuous length of service on the court, and such associate justice of the Supreme Court is hereby authorized and empowered to perform all of the same in lieu of the chief justice during the latter’s disability or absence from the court for said period longer than 30 days.