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BELL SYSTEM TECHKICAL JOURNAL 



through the water. By rigid observance of such precautions no 

 difficulty should be experienced in securing accurate records by means 

 of this recorder. 



L.'\BORATORY TeSTS 



Several of these recorder mechanisms were built and after having 

 been adjusted to operate satisfactorily, each wind tunnel equi[iment 

 connected to its associated recorder was placed in a laboratory room 

 controlled by air conditioning equipment, and given a run to test its 

 operation under the range of conditions which might be expected to 

 occur at the localities where the recorders were to be installed. During 

 this test, the readings given by the recorder were compared with 

 those obtained with a \entilated psychrometer. Fig. 4, equipped with 

 accurate wet and dry bull) thermometers. Table I following gives a 

 summary- of the readings obtained in calibrating one of the recorders, 

 while P'ig. 5 shows a typical 12 hour record obtained in one of the 

 laborator\- rooms. 



T.ABLE 1 



Reference to tlusc laiuilatcd wilucs of relative humidilies obtained 

 by the two methods indicates that the recorder is capable of giving 

 reliable data particularly through the range of high humidities where 

 the effects on materials or apparatus exposed to these conditions may 

 be large. Difficultx- was experienced in comparing the readings of 

 the two instruments due to the sensitivity of the resistance ther- 

 mometers to slight temperature changes, and also due to the slight 

 differences in tem[)erature between the two sets of thermometers which 

 necessarily occurred Injcause they were not in the same wind tunnel. 

 This difficulty was encountered particularly when the "humidity 



