BOTTOM AIR. 39 
brickwork, as shown in Fig. 23. A 9in., or 12in. board, lin. 
or 1liin. thick, cut into lengths of 4ft. or 5ft., strengthened by 
a couple of cross braces apiece, and hung between the two 
plates, will answer admirably. 
For small structures, or where only a small amount of 
bottom air is required, even ordinary Tin. floor boards will 
be found quite sufficient. These may be hung with Paine’s 
LA 
Fig. 23. 
or Piper’s patent hinges, and opened and closed by means of 
small casement stays, with a button to secure each when 
closed, or gearing may be fitted to them, but in this case 
short arms and levers should be employed. 
I have used ventilators of this kind in several instances 
with great success and satisfaction ; they occupy but little 
room, and at the same time admit abundance of air, while 
they present a very neat and pleasing appearance. 
