70 SCIENCE I:N T SHORT CHAPTERS. 



by the dimensions 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 converts the 

 whole house into an upcast shaft, and the whole outer atmos- 

 phere becomes a downcast. In the summer time, the kitchen 

 tire 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 inclosed within the chimney, a 

 small automatic slow-combustion stove (of which many were 

 exhibited at South Kensington, that require feeding but once 

 in twenty-four hours), or a large gas-burner. The heating- 

 chamber below must now be converted 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 tempera- 

 ture. 



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 the rooms 

 supplied with air from above down the house shaft, through 

 the rooms, and out of the kitchen via the winter heating- 

 chamber, which now has its communication with the outside 

 air closed. 



Reverting to the first-named method, which I think is better 

 than the second, besides being less expensive, I must say a few 

 concluding words on an important supplementary advantage 

 which is obtainable wherever all the air entering the house 

 passes through one opening, completely under control, like that 

 of our heating-chamber. The great evil of our town atmos- 

 phere is its dirtiness. In the winter it is polluted with soot 

 particles ; in the dry summer weather, the traffic and the wind 

 stir up and mix with it particles of dust, having a composition 

 that is better ignored, when we consider the quantity of horse- 

 dung that is dried and pulverized on our roadways. All the 

 dust that falls on our books and furniture was first suspended 

 in the air we breathe inside our rooms. Can we get rid of any 

 practically important portion of this ? 



I am able to answer this question, not merely on theoretical 

 grounds, but as a result of practical experiments described in 

 the following chapter, in which is reprinted a paper I read at 



