Ventilators 111 



a N ventilator in the highest part of the roof, 

 which will permit the heated air to escape. It 

 is rarely necessary to provide special means for 

 cold air to enter, as there is usually a sufficient 

 number of cracks about doors and windows to 

 admit cold air if means be provided for the lighter 

 air to escape. Fig. 38 illustrates the construc- 

 tion of a cheap and effective ventilator. This 

 may be readily closed and opened by means of 

 cords or chains as the attendant passes through 

 the house. 



