The headquarters and general offices of said commission shall be located at some city or town on the Mississippi River, to be designated by the Secretary of the Army, and the meetings of the commission except such as are held on Government boats during the time of the semiannual inspection trips of the commission shall be held at said headquarters and general offices, the times of said meetings to be fixed by the president of the commission, who shall cause due notice of such meetings to be given members of the commission and the public.