THE MONTHLY BULLETIN. 559 



EXPERIMENT I. 



Stationary instrument placed in a sheltered position so that there was no draft of 

 air on it, the sling psj'chrometer being whirled in the usual way. 



Dry bulbs when placed together registering within less than one degi-ee of each 

 other : 



Stationary hygrometer — 



95° dry bulb 

 83° wet bulb 



Depression 12° indicates 60.5 per cent relative humidity. 

 Sling psychrometer — 



98° dry bulb 

 72° wet bulb 



Depression 26° indicates 27 per cent relative humidity. 

 Difference between the two hygrometers 33.5 per cent relative humidity. 



EXPERIMENT II. 



Same hygrometer placed directly in a current of air from an electric fan : 



Stationary hygrometer — 



99.5° dry bulb 

 79.5° wet bulb 



Depression 22.0° indicates 41 per cent relative humidity. 

 Sling hygrometer — 



98° di-y bulb 

 72° wet bulb 



Depression 26° indicates 27 per cent relative humidity. 

 Difference between the two hygrometers 15 i>ev cent relative humidity. 



The wicking on the stationary in.striimeut did not wet uniformly, the 

 pores being considerably clogged. From these experiments it will be 

 seen that when the two types are placed in uniform conditions the 

 stationary form is not as accurate, unless kept in perfect condition. 



The sling psychrometer, although not as convenient as other forms, 

 is recommended on accoimt of its accuracy. These instruments can be 

 gotten from most of our supply houses dealing with scientific instru- 

 ments. The psychrometer is furnished with certified thermometers and 

 sells for eight or nine dollars. Cheaper thermometers can be used, but 

 it is well to have the more accurate ones ; then the instrument can be 

 used for correcting other forms of hygrometers or the cheaper ther- 

 mometers. 



