After consent of the majority of those voting on the question at any general or special election in cities of the first or second class, the cities may annually thereafter, levy a tax on the assessed value of real and personal property, not to exceed two mills on the dollar, from which there shall be created a Fund to pay Retirement Salaries and pensions to policemen and firemen theretofore or thereafter earned, and pensions to the widows and minor children of such, as may be provided by law. The annual levy for the Policeman's Retirement Salary and Pension Fund shall not exceed one mill on the dollar, and the annual levy for the Fireman's Retirement Salary and Pension Funds, shall not exceed one mill on the dollar. The manner of such levy of the tax, and the eligibility for the retirement salaries and pensions, the several amounts thereof and when payable, shall be such as may be provided by law.