A majority of the members elected to each house shall constitute a quorum to do business, but a smaller number may adjourn from day to day and shall have power to compel the attendance of members in such manner and under such penalty as each house may prescribe. A smaller number, not less than two-fifths of the elected membership of each house, may meet and may, notwithstanding any other provision of this Constitution, enact legislation if the Governor by proclamation declares that a quorum of the General Assembly cannot be convened because of enemy attack upon the soil of Virginia. Such legislation shall remain effective only until thirty days after a quorum of the General Assembly can be convened.