Section 1. The County Board of School Trustees in counties having a population of not less than sixteen thousand, six hundred and seventy (16,670) nor more than seventeen thousand and sixty (17,060) and all counties having a population of not more than nine thousand, four hundred and five (9,405) and not less than nine thousand, three hundred (9,300), according to the last preceding Federal Census, may employ, upon the recommendation of the County Superintendent, a rural school music supervisor to plan, outline, supervise, and teach music in the rural schools which are under the supervision and administration of the County Superintendent of Public Instruction, said supervisor at all times to work in cooperation with and under the supervision of the County Superintendent of Public Instruction. Such supervisor must have evidence of proficiency in public school music and be able to direct same. Other qualifications to be set up by County Superintendent.