3 o POPULAR SCIENCE MONTHLY 



smoke from the engines, subway cars with dust-laden air from the 

 tunnel, is naturally inefficient and of questionable benefit. Efficiency 

 in ventilation must come through wider streets and courts, cleaner 

 thoroughfares, the abolition of smoke and dust nuisances, and last, but 

 not least, through the design of buildings, engineering work, public 

 conveyances and their equipment on sanitary lines. 



Laws have been in effect in several states which prescribe a fixed 

 amount of fresh air to be supplied per capita in schools and theaters. 

 These laws do not cover the standard of purity, except perhaps as ex- 

 pressed by the carbonic acid test, which does not measure the worst 

 forms of contamination. They do not always define temperature and 

 other qualities essential to secure its benefit to people. Moreover, it is 

 almost hopeless to enforce them in the proper spirit. Discretion might 

 often be in order where natural conditions will help, but can not be 

 conceded while the exact volume of artificial supply is prescribed. The 

 chief benefit of such legislation lies in its educational effect on people. 

 The urgent need to-day is to bring before the public again and again 

 the most objectionable causes of impure air, especially those of pre- 

 ventable nature, and to promote sound judgment as to the logical and 

 practical means of relief. 



Ventilation can be effected by natural, artificial or mechanical 

 means. Each of these three methods has its field for application. 

 Natural ventilation is incidental to the design and construction of a 

 building. Frame houses are subject to considerable leakage through 

 the shrinking wood-work of walls, windows and doors and through their 

 greater exposure to the air generally. Such ventilation may also be 

 called spontaneous. It is generally sufficient in exposed wooden dwell- 

 ings, at times even greater than necessary. Brick and stone buildings 

 are also subject to more or less spontaneous ventilaton, which, however, 

 does not always meet the need. In such cases, the general design of 

 the building should be arranged deliberately to encourage a natural 

 ingress and egress of air. For residences and offices not unduly 

 crowded, this may suffice with a fair exposure, but often it should be 

 supplemented by artificial means. This implies that the building must 

 have certain features which induce a decided movement of air, such as 

 shafts leading from kitchen and inside rooms, also fire-place flues and 

 vents from special sources of odor. With such provisions an active 

 removal of foul air may be effected by differences of temperature, in- 

 creased possibly by waste heat available. The leading idea should be 

 to give the most advantageous direction to the natural currents of air. 

 Systematic supply of fresh air, combined in some form with the heating 

 apparatus, is appropriate in many cases, particularly as it permits some 

 control over the purity, temperature and humidity of the air entering 

 the building. 



