of water in the conduits, provided with louvres for deflecting the particles of dust floating in the air. A good form of heating small libraries by hot air is that provided by means of "Gill" stoves placed in the different rooms, but these necessitate the carrying of fuel and ashes to and fro, and so are undesirable for large libraries.
The British Museum is heated by hot air obtained through a shaft some sixty feet high. The air is drawn along by a rotary fan and heated over boilers, it then passes through a chamber provided with sprays of water for counteracting dryness. Under the central reading-room is a vast air-chamber, divided into long, narrow compartments, which radiate from the centre to the circumference, and each provided with hot-water pipes. The hot air enters the reading-room from inlets in these chambers, arranged at the end and top of each row of readers' desks. The room is lit by side windows and a lantern, the latter being double to protect the readers from draughts caused by the chilling of the hot air against the glass, and the upward current of the vitiated air is helped by means of coils of steam-pipes placed in the dome. The exits are the ordinary "Boyle" ventilators. Much of the success of the Museum heating depends upon the efficiency of the engineer. Without constant and unfailing watchfulness this extensive building would be most difficult to keep at an even temperature. As it is, complaints are not wanting. On one occasion a reader propounded to a stoker a theory of heating, founded upon the
