(5) In =Louvre Ventilators=, a number of parallel pieces of glass, each directed upwards, are substituted for a pane of glass. They may be fixed or made movable, as in Moore’s ventilator. The incoming current of air may be similarly directed upwards, in an open window, by arranging Venetian blinds with the laths inclined upwards. (6) In windows that will not open, =Cooper’s Ventilators= are often used. Each of these consists of a circular disc of glass, having five oval apertures in it, which works on a pivot through its centre, close in front of one of the panes of a window, which has five similar holes pierced in it. Consequently, when the disc is turned, so that its holes are opposite those of the window, fresh air is admitted. The amount thus admitted is necessarily small. =The Chimney= forms the best means of escape of foul air. No room ought to be built without a fire-place, which should never subsequently be boarded up. In bedrooms the chimney forms a most important means of ventilation. If there is no fire, the chimney occasionally furnishes an undesirable source of air; but as a rule the current is upwards, owing to the aspirating action of winds at the top of the chimney. The downfall of air from a chimney chiefly occurs when there is an insufficient inlet for pure air. This is the explanation of =smoky chimneys= in nine cases out of ten; then the cure is easy by laying on a pipe from the outside of the house to the hearth. When the smoky chimney is due to the contiguity of higher buildings, the chimney must be raised, or a cowl placed over it. (1) The action of the chimney in carrying impure air away from the room may be considerably increased by =narrowing the two ends=, so as to produce a more rapid current at the entrance and exit of air. (2) The heat of the chimney may be utilised by having a =separate smaller flue= alongside it, with openings from the rooms on each floor. The air in this being heated aspirates the air from each room in succession. Openings may be made into the chimney-flue at a higher point than the fire-place. These are very valuable for carrying off the heated and impure air resulting from the combustion of gas, as well as for carrying off the respiratory products, which, in their warmed condition, tend to rise towards the ceiling. (3) =Dr. Neil Arnott= first devised a valve for this purpose. An opening being made through the upper part of the wall into the chimney, an iron box was inserted, in which was placed a light metal valve capable of swinging towards the chimney flue, but not towards the room. The objections to this apparatus are that it is apt to make irregular clicking noises, and to admit blacks from the chimney when out of order.