206 



ELEMENTARY SCIENCE 



placed in the basement in an enclosure through which air 

 passes over them. This air, when heated, is delivered by 

 flues to the rooms above. Very satisfactory results may 

 be obtained by such an indirect system (see Fig. 78). 



Ventilation. You have already noted that the chief 

 difficulty in ventilation is that it works at cross-purposes 

 with heating; it is hard to ventilate a building properly 



and at the same time to 

 heat it sufficiently. In late 

 years, however, it has been 

 proved that, to make bad 

 air good, it may not be nec- 

 essary to change it. In other 

 words, bad air may be made 

 good by washing it and stir- 

 ring it. This is done by 

 driving it through a screen 

 of falling water, whereby 

 the disease-germs and other 

 FIG. 7 s.-The indirect heating system, impurities are removed. 



Such ventilation systems 



have not come into general use, but they are successfully 

 and economically operated in a number of places. 



There is little doubt that the frequent colds that peo- 

 ple catch in winter, and which so frequently lead to seri- 

 ous or even fatal illnesses, are largely due to poor ventila- 

 tion. In badly ventilated rooms, especially in those used 

 by the general public, disease-germs accumulate and mul- 

 tiply. Good ventilation would drive them out, or reduce 

 their number below the danger-point. Bad ventilation 

 particularly promotes tuberculosis, which is one of the 



