Whenever a judge shall have knowledge of any fact which, under the provisions of section 284 of this title, disqualifies him to sit or act as such in any action or proceeding pending before him, it shall be his duty to declare the same in open court and cause a memorandum thereof to be entered in the minutes. It shall thereupon be the duty of the clerk to transmit forthwith a copy of such memorandum to each party or his attorney who shall have appeared in such action or proceeding, except such parties as are present in person or by attorney when the declaration is made.