Section 1. Be it enacted, &c., That the councils of each city in this commonwealth are empowered from and after the passage of this act, from time to time, to fix by ordinance the salary to be paid out of the city treasury to the mayor of such city: Provided, That nothing herein contained shall authorize a change in the salary, fees or emoluments of the mayors now in office, and those elected prior to the passage of this act.