Section 1. That the County Board of School Trustees in counties having a population of not less than 31,000 nor more than 31,789, according to the Federal Census of 1920, and a scholastic population of not less than 9,300 as shown by the scholastic report for the school year of 1928-29, may employ a Rural School Supervisor to plan, outline, and supervise the work of the primary and intermediate grades of the rural schools of the county.