He may, on extraordinary occasions, convene the General Assembly at the seat of government, or at a different place, if that should have become dangerous from an enemy or from contagious diseases. In case of disagreement between the two Houses with respect to the time of adjournment, he may adjourn them to such time as he shall think proper, not exceeding four months. When he shall convene the General Assembly it shall be by proclamation, stating the subjects to be considered, and no other shall be considered.