The powers and duties of the lieutenant governor shall be to serve as president of the senate, and he may, when the senate is equally divided, vote on procedural matters, and on substantive matters if his vote would be decisive. Additional duties shall be prescribed by the governor. If, during the vacancy in the office of governor, the lieutenant governor shall be impeached, displaced, resign, or die, or from mental or physical disease, or otherwise become incapable of performing the duties of his office, the secretary of state shall act as governor until the vacancy shall be filled or the disability removed.