474 THE MECHANICS OF VENTILATION. 



4. There is a relation between inside temperature, outside temperature 

 and outside humidity, which relation appears to be expressed by saying that 

 inside temperature varies directly as outside humidity and inversely as out- 

 side temperature. 



The writer cannot at present vouch for the entire correctness of this last 

 !aw ; the observations were somewhat conflicting, though the preponderance 

 is decidedly in favor of the law. It stands at present, however, as an infer- 

 ence rather than a positive induction. 



The temperatures show invariably an increase from beginning of school 

 in morning (9 A. M.) to end of first hour (10 a. m.). They also show a cor- 

 responding increase from beginning of school in afternoon (1.30 p. m.) to end 

 of first hour (2.30 p. m.). In buildings of no ventilation, and where, dur- 

 ing the winter, flushing with fresh air is resorted to by opening windows at 

 intermissions, the thermometers were naturally lower after intermission 

 than before; while in those where flushing is not resorted to, the tempera- 

 tures were substantially the same. The maximums were usually obtained 

 before intermission and at end of session. Observations on humidity were 

 also taken in several of the buildings, and it was found that a great increase 

 of moisture in excess of that outside took place in poorly-ventilated rooni!^? 

 pointing to the conclusion that excess of temperature is accompanied by 

 ■excess of moisture, and to the farther consideration that excess of tempera- 

 ture and excess of moisture are certain indications of defective ventilation. 



Judging from the showing of the temperature records a great difference 

 •of opinion exists as to the proper temperature at which a room should be 

 kept. The rooms are undoubtedly kept at the point of comfort and that 

 point varies as perfection of ventilation varies. For instance, the lowest 

 temperatures occur in well-ventilated rooms, while the highest occur in those 

 poorly ventilated. In rooms where the temperature ranges from 62° to 66° 

 the question was asked of the teachers in at least twenty places, "Do you 

 find the room too warm when much above 66° ?" The reply usually was, 

 "We do." In the case of rooms with an average temperature of 68°-71° the 

 form of question was, "Do you find the room too cold when much below 

 '68° '?" The reply was in nearly every case, "We do." The general princi- 

 ple, therefore, is, in imperfect ventilation the exhalations from the body and 

 breath produce an excess of moisture in the air, and, consequently, an increase 

 ■of relative humidity. Our sensations of heat and cold depend (within limits) 

 as much upon the amount of moisture present in the air as upon the actual 

 temperature. A high relative humidity always produces chilliness. We in- 

 stinctively, therefore, increase the heat as the moisture increases. Moreover 

 the air's capacity for moisture increases as the temperature. In illy-ventil- 

 ated apartments, the two go together, increase of moisture leading to increase 

 of heat, increase of heat leading to increase of moisture. Aside from the 

 mere waste of heat resulting from this condition of affairs, there is matter 

 of more serious import to be considered. Where bad ventilation exists 

 the windows and doors are thrown wide open for flushing at intermissions 



