APPENDIX TO EXERCISE XV 129 



THE HYGRODEIK 



With this instrument the Relative Humidity of the air may be 

 determined without the use of tables. See Exercise XV. 



To find the Relative Humidity swing the index hand to the 

 left of the chart, and adjust the sliding pointer to that degree of 

 the Wet Bulb Thermometer Scale at which the mercury stands. 

 Then swing the index hand to the right, until the sliding pointer 

 intersects the curved line which extends downward to the left 

 from the degree of the Dry Bulb Thermometer Scale at which 

 the mercury stands. At this intersection the index hand will 

 point to the Relative Humidity on the scale at the bottom of 

 the chart. 



Example: The temperature indicated by the Wet Bulb Ther- 

 mometer is 60, and that of the Dry Bulb 70. The index hand 

 will indicate the Relative Humidity 55 whon the pointer rests 

 on the intersecting lines of 60 and 70 degrees. 



