Where in any county in this State bonds of any such county and the levy of an additional tax in excess of the statutory limit but within the constitutional limit for payment of such bonds have been authorized for any proper county purpose to enable the county board to perform any of the duties imposed upon them by law by a majority of the legal voters voting on the question of issuing such bonds and levying such additional tax at an election held since November 1, 1947, and subsequently resolutions have been adopted authorizing such bonds as voted and levying direct annual taxes sufficient to pay the principal of and interest upon said bonds and a certified copy of such resolutions have been filed in the office of the county clerk of said county, and due to the increase in interest rates on public borrowings in the financial markets of the country since such election, such voted additional tax is not sufficient to pay the principal of such bonds and interest thereon, the county clerk of any such county is authorized hereafter to extend for collection a tax upon all the taxable property therein, in addition to such voted additional tax, at a rate on the one hundred dollar valuation which, when extended, will produce an amount sufficient to pay the principal of and interest upon said bonds as authorized and levied in said bond resolutions, provided such additional tax shall not be in excess of the constitutional limit of taxation applicable to counties.