When a vacancy occurs, by death or otherwise, in the head or chief of any of the departments of the State Government, and the duties thereof devolve upon and are discharged by the deputy, chief clerk, or person next in authority, for a period of one month or more, such deputy, chief clerk, or other person next in authority, shall be paid an amount, over and above his regular salary, that shall equalize it with the salary provided by law to be paid to the head or chief of such department for and during the time he has performed the duties of head or chief of such department.
71 P.S. § 764