MANAGEMENT OF THE ATMOSPHERE. 293 



provided with valves to open and shut at pleasure, to any extent 

 within the limits of their diameter, so that the apertures of 

 ingress for the cold air may be regulated by the operator accord- 

 ing to the state of the weather and the quantity of air required. 

 The size of these tubes will Depend upon the size and situation 

 of the house. For instance, if the house contains a large inter- 

 nal volume of atmosphere, the perforated tube would require to 

 be at least eight inches in diameter, and the smaller about one 

 half the size of the large ones. And now for its mode of action. 

 It will be evident, that when fire is applied to the furnace, its 

 cover (which forms the floor of the chamber) will become heated 

 to a considerable degree. As soon as this takes place, the 

 external valve of the drain, which communicates with the main 

 tube, should be opened, when the external air will immediately 

 rush in ; and, by having to traverse the heated floor of the 

 chamber aforesaid, will expand along the large tube connected with 

 it, which, from being in contact with the heated air, will itself 

 become warm. The radiation of heat, too, from the surface of 

 the flue directly beneath it, will assist in maintaining the tem- 

 perature of the tube ; so that, although a portion of the heated 

 air will escape through the perforations in its upper surface, 

 enough will be retained to effect the purpose intended, which is, 

 to neutralize the effects of the cold air that will be admitted 

 through the medium of the small lateral tubes, and which may 

 be admitted in any quantity, to the full volume of their admis- 

 sion. As the warm air rushes along the tube, it will mingle 

 with that admitted by the small tubes; and the cold air, enter- 

 ing by the latter, will thus be modified, while a supply of fresh 

 air will at the same time be circulated through the atmosphere 

 of the house. 



8. The advocates of what has been called a " free system of 

 ventilation" have, like many others, in practising and advocat- 

 ing a favorite theory, in their excess of zeal, completely defeated 

 the objects they sought to secure. The sole object of some of 

 the advocates of the free system appears to be the prevention 

 of a stagnant atmosphere. They admit an unlimited quantity 

 of atmospheric air, at all seasons, to prevent this most terrible 



