Each circuit judge in the Fifteenth Judicial Circuit, in addition to the salary paid by the state, shall receive a supplemental salary from the general fund of the county composing the judicial circuit. The supplemental salary shall at all times equal 40 percent of the salary paid each judge by the State of Alabama and shall be paid in equal installments at the same times and in the same manner that the salaries of the county employees are paid. The governing body of the county is hereby authorized, empowered, and directed to pay the supplemental salary provided herein to each circuit judge out of the funds of the county or any other funds as may be available for such purpose. The salary provided herein is in lieu of any other supplemental salary paid by the county and represents the total supplemental salary to be provided by the county for such judges.