320 VENTILATION 



which is uncomfortably low in the evening when our vitality 

 is lowest. Still another factor affecting the most agreeable 

 temperature of air is that of air movements. Air in rapid 

 motion must be a few degrees warmer than quiet air in order 

 that we may be comfortable. Why? (See Art. 318.) 



The best temperature, then, depends upon many factors 

 such as the occupation, dress, physical condition, and tempera- 

 ment of the occupants of the room, on the one hand, and the 

 humidity and movements of the air, on the other hand. The 

 effect of air motion and of high or low humidity should be 

 further studied. 



351, Some Fluctuation in Temperature is Desirable. A 

 German, Fliigge, seems to have proved that a perfectly uniform 

 temperature is not desirable. Many students of ventilation 

 now maintain that reasonable fluctuations in temperature are 

 necessary to stimulate us and to keep our physical and mental 

 powers alert, awake, and active. A perfectly uniform tempera- 

 ture, even though it be the most agreeable, lacks the stimu- 

 lating effect of a reasonably fluctuating temperature (see 

 Arts. 219, 324 and -335.) 



352. Effect of Air Movement. Dr. Leonard Hill of London 

 and others, have shown that proper air movement is a large 

 factor in ventilation. Dr. Hill placed eight healthy medical 

 students in a small, air-tight, glass-sided box, or cage, 4}^ ft. 

 square and 8 ft. high. In a few minutes they became very 

 uncomfortable. The temperature of the air in the cage had 

 risen to 85F. and had become nearly saturated with 1 * moisture. 

 The air then contained about 4 per cent, of carbon dioxide and 

 but about 15 per cent, of oxygen. Three electric fans in the 

 top of the cage were then set in motion, causing the air to more 

 rapidly. The students were soon greatly relieved and became 

 again comfortable, although the composition and the temper- 

 ature of the air remained unchanged. 



Students of ventilation generally agree that quiet air, no 

 matter how pure it may be or what its temperature and rela- 

 tive humidity may be, does not furnish adequate ventilation 



