The mayor and councilmen, before entering upon the duties of their respective offices, shall take the oath prescribed by the Constitution and also the following oath, to wit:
"As mayor (councilman) of the municipality of __________ I will equally, fairly, and impartially, to the best of my ability and skill, exercise the trust reposed in me, and I will use my best endeavors to preserve the peace and carry into effect according to law the purposes for which I have been elected. So help me God."