Sec. 2. COUNTIES OF 77,750 TO 77,800. In counties having a population of not less than seventy-seven thousand, seven hundred and fifty (77,750) and not more than seventy-seven thousand, eight hundred (77,800), according to the last preceding Federal Census, the salary of the county superintendent of public instruction shall be Three Thousand, Six Hundred Dollars ($3,600) per annum. Such salary shall be paid in accordance with existing laws governing such office.