This section is from the book "The National Capitol. Its Architecture Art And History", by George C. Hazelton, Jr. Also available from Amazon: The National Capitol Its Architecture Art and History.
The Capitol and grounds are under the authority of a Police Board, composed of the Sergeant-at-Arms of the Senate, the Sergeant-at-Arms of the House and the Architect of the Capitol. This board acts through a Captain of Police, customarily assisted by three lieutenants and a corps of privates, who are directly responsible for the protection and peace of the building. The supreme authority in the Senate wing is always vested in the Vice-President of the United States, who presides over the Senate ; the Supreme authority in the House wing, in the Speaker of the House of Representatives; and the supreme authority in the old building, in the Architect of the Capitol.