The Governor may, by proclamation, on extraordinary occasions, convene the General Assembly at the seat of government, or at a different place, if that shall have become, since their last adjournment, dangerous from an enemy or contagious disease; and he shall specify in his proclamation the purpose for which they are convened; and no other business than that set forth therein shall be transacted until the same shall have been disposed of; after which they may, by a vote of two-thirds of all the members elected to both houses, entered upon their journals, remain in session not exceeding fifteen days.