from the book "THE PRINCIPLES OF MASONIC LAW"
A Treatise on the Constitutional Laws, Usages And Landmarks of Freemasonry
by Dr.Albert Gallatin Mackey, 1856
It is the prerogative of the Master to appoint all Committees, unless by a special resolution provision has been made that a committee shall otherwise be appointed.
The Master is also, ex officio, chairman of every committee which he chooses to attend, although he may not originally have been named a member of such committee. But he may, if he chooses, waive this privilege, yet he may, at any time during the session of the committee, reassume his inherent prerogative of governing the craft at all times when in his presence and therefore take the chair.