Ill' Mini I y KIXOKIU.KS 247 



From the data aicunuilatod in those cities, comprehensive informa- 

 tion has l)cen <ibtaine<l as to the (hiration of conditions of average 

 and maximum se\erity which occur during; the iumiid months. It ii» 

 of interest to compare the vahies of the central otlice conditions of 

 temperature and relative humidity otitained from tlie recorders, with 

 the corrcspondini; W'ealliiT Bureau observations. The curves given 

 in Fig. t) show a typical comparison from (lata obtained at Sa\annah, 

 Ga., during May, 1922. Study of these curves shows that the indof)r 

 tem(H'rature averaged somewhat higher than that out of doors, and 

 that the indoor relati\e humidities were seldom higher than 75%, 

 although the outdoor humidities often were higher than 8.5% for 

 considerable lengths of time. The Weather Bureau data indicate 

 very definitely when rain storms occurred and also periods of high 

 humidity, due perhaps to foggy weather, although such perifKJs are 

 not well defined by the humidity curves showing the indoor conditions. 



Since for a gi\en absolute humidit>', the relative humidity \'aries 

 inversely with the change in temj)erature of the air, obviously it 

 should be possible to keep the relative humidity in a central office 

 building lower than that of the outside air by keeping the windows 

 closefl during periods of sudden temperature changes, and by the use 

 of heat in switchboard sections. This latter remedy for humidity 

 troubles has been successfully applied for several years to switch- 

 boards installed in some localities. Also the effects upon the indoor 

 humidity and upon the performance of central office equipment, of 

 closing the windows of central office rooms has been the subject 

 of considerable investigation. 



In the study of this method of reducing relative humidity, it is 

 very desirable to have records which will show continuously the dif- 

 ferences existing between indoor and outdoor temperatures and 

 relati\e humidities, and in particular to study the effects on the 

 indoor conditions when sudden changes in atmospheric conditions 

 occur such as rain storms when the relative humidity outside reaches 

 10()%. It was found that the automatic recorder described above 

 would lend itself admirably tf) the study of this problem and that 

 by the use of a simple relay switching mechanism on the recorder, 

 two wind tunnel equipments could be operated with one recorder, 

 enabling temperatures and differences between dry. and wet bulb 

 temperatures to be recorded alternately on the same chart for both 

 indoor and outdoor conditions. 



A recorder of this type was operated during the summer months 

 of 1921 at the West Street laboratories of the Western Electric Co., 

 Inc., to record the conditions in a well ventilated laboratory room 



