in the first, and multiplied by 2, to obtain THE 



ANSWER PUT DOWN IN THE THIRD COLUMN. 



EXAMPLE. Temperature of the air 57, wet bulb 

 54 = 3 degrees of dryness observed ; then add 0.5 

 excess of dryness = 3.5 and multiply by 2, which 

 will give 7 degrees of absolute dryness existing. 



To find the dew-point Subtract the absolute 

 dryness from the temperature of the air. Example 

 57 7 50 dew-point. 



To find the actual quantity of vapor by weight 

 in the atmosphere. Proceed as directed in the 

 TABLE OF QUALITY. 



The comparison of Mason's with the *Dew- 

 point Hygrometer, and of Sir John Leslie's, will 

 be seen in the same line of the ist, 3d and 4th 

 columns of the Table. 



TO FIND THE QUANTITY OF TAPOR BY WEIGHT 

 EXISTING IN THE ATMOSPHERE. 



PROBLEM. The Temperature of the Atmos- 

 phere in the shade, and of the dew-point being 

 given, to find the quantity of vapor in a cubic foot 

 of air. 



If the temperature of the air and the dew-point 

 correspond, which is the case when both ther- 

 mometers are alike, and the air consequently satu- 

 rated with moisture, then in the table of quantity 

 opposite to the temperature, will be found the cor- 

 responding weight of a cubic foot of vapor ex- 

 pressed in grains. 



* Professor Daniel's Hygrometer is registered by the 3d column. 

 124 



