Any township, city or village within this state, having within its limits a library that had been open to the public upon the payment of dues, may appropriate not to exceed 1/2 of 1 mill on its assessed valuation for the support of such library, and such sum or sums shall be raised by taxation in the ordinary way: Provided, That any library so receiving support from any municipality shall be kept open for the convenience of the public not less than the afternoons and evenings of 3 days of each week, and the books therein shall be for the free use of the public under such reasonable restrictions as such library shall prescribe.