In arranging for the removal of foul air it is necessary, particularly in the downward system, to provide separate exhaust flues for the galleries and balconies. Unless this is provided for, the exhaled air of the occupants of the higher tiers would mingle with the descending current of pure air supplied to the occupants of the main auditorium floor. Mention should also be made of a proposition originating in Berlin to construct the roof of auditoriums domelike, by dividing it in the middle so that it can be partly opened by means of electric or hydraulic machinery; such a system would permit of keeping the ceiling open in summer time, thereby rendering the theater not only airy, but also free from the danger of smoke. A system based on similar principles is in actual use at the Madison Square Garden, in New York, where part of the roof consists of sliding skylights which in summer time can be made to open or close during the performance. From the point of view of safety in case of fire, which usually in a theater breaks out on the stage, it is without doubt best to have the air currents travel in a direction from the auditorium toward the stage roof. This has been successfully arranged in some of the later Vienna theaters, but from the point of view of good acoustics, it is better to have the air currents travel from the stage toward the auditorium. Obviously, it is a somewhat difficult matter to reconcile the conflicting requirements of safety from smoke and fire gases, good acoustics and perfect ventilation. The stage of a theater requires to be well ventilated, for often it becomes filled with smoke or gases due to firing of guns, colored lights, torches, representations of battles, etc. There should be in the roof over the stage large outlet flues, or sliding skylights, controlled from the stage for the removal of the smoke. These, in case of an outbreak of fire on the stage, become of vital importance in preventing the smoke and fire gases from being drawn into the auditorium and suffocating the persons in the gallery seats. Where the stage is lit with gaslights it is important to provide a separate downward ventilation for the footlights. This, I believe, was first successfully tried at the large Scala Theater, of Milan, Italy. The actors' and supers' dressing rooms, which are often overcrowded, require efficient ventilation, and other parts of the building, like the foyers and the toilet, retiring and smoking rooms, must not be overlooked.