Special meetings of Council may be called by a vote of Council taken at any regular or special meetings; or special meetings may be called by the Mayor and shall be called by the Clerk of Council upon the written request of three members of Council. Any such vote or request, for the calling of a special meeting, shall state the subject or subjects to be considered at the meeting and no other subject or subjects shall be there considered, except on the approval of five (5) or more of the members of Council in attendance at the special meeting. Twelve (12) hours notice in writing of such special meeting, shall be given to each member of Council and the Mayor by personal service, or by leaving same at their usual places of residence; except that the members of Council shall be held to have waived such notice by their attendance at the special meeting.