348 SCIENCE IN SHORT CHAPTERS. 



bodily become an upcast shaft immediately the inner tem- 

 perature exceeds that of the air outside. 



But the upcast of warm air can only take place by the 

 admission of fresh air through the heating chamber, thence 

 to hall and staircase, and thence onward through the rooms 

 into the final shaft or chimney. 



The openings into and out of the rooms being adjustable, 

 they may be so regulated that each shall receive an equal 

 share of fresh warm air; or, if desired, the bedroom chim- 

 ney valves may be closed in the daytime, and thus the heat 

 economized by being used only for the day rooms; or, vice 

 versa, the communication between the upcast shaft and the 

 lower rooms may be closed in the evening, and thus all the 

 warm air be turned into the bedrooms at bedtime. 



If the area of the entrance apertures of the rooms exceeds 

 that of the outlet, only the latter need be adjusted; the 

 room doors may, in fact, be left wide open without any 

 possibility of "draught," beyond the ventilation current, 

 which is limited by the dimension of the opening from the 

 room into the shaft or chimney. 



So far, for winter time, when the ventilation problem is 

 the easiest, because then the excess of inner warmth con- 

 verts the whole house into an upcast shaft, and the whole 

 outer atmosphere becomes a downcast. In the summer 

 time, the kitchen fire would probably be insufficient to 

 secure a sufficiently active upcast. 



To help this there should be in one of the upper rooms 

 say an attic an opening into the chimney secured by a 

 small well-fitting door; and altogether enclosed within the 

 chimney a small automatic slow-combustion stove (of which 

 many were exhibited in South Kensington, that require 

 feeding but once in twenty-four hours), or a large gas- 

 burner. The heating-chamber below must now be con- 

 verted into a cooling chamber by an arrangement of wet 

 cloths, presently to be described, so that all the air entering 

 the house shall be reduced in temperature. 



Or the winter course of ventilation may be reversed by 

 building a special shaft connected with the kitchen fire, 

 which, in this case, must not communicate with the house 

 shaft. This special shaft may thus be made an upcast, and 



