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 engines, in the basement of the Capitol, bring air into the building through tunnels extending from two granite towers situated in the park; and by means of large fans it is then driven through the building, heated in winter and cooled and moistened in summer. Fans also carry off the vitiated air. The official statements show that, from March 3, 1831, to 1875, trie net expenditures for heating and ventilating the Capitol were $298,-584.39; and that between March 3, 1855, and June 1, 1875, the heating of the Library netted $17,071.60.
The chambers of the Senate and House are lighted almost exclusively from above, through double glass roofings by day and by incandescent lights by night, which burn brightly between the ceilings and produce soft and beautiful effects throughout the rooms. Above the Senate Chamber are 1,200 lamps with 842 outlets of sixteen candle power each, making a total candle power of 19,200. Above the House Chamber are 1,388 lamps with 1,192 outlets of sixteen candle power each, making a total of 22,208 candle power. The net expenditures for lighting the Capitol from March 3, 1829, to March 3, 1875, are given by the Treasury Department as $1,335,757.70.