37 



Rule. 



Multiply the difference between the two thermo- 

 meters by the factor corresponding to the temperature 

 of the dry-bulb thermometer, and subtract the product 

 from it ; the remainder will be the temperature of the 

 dew- or vapour-point. 



o 



Let dry-bulb thermometer =66 

 Let wet-bulb thermometer = 57 



Difference = *9 

 1-8 



Product =16-2 

 66 - 16-2 = 49-8 = dew-point. 



Dr. Apjohn's formula for finding dew-point is 



Above 32. Below 32. 



ftt-f\__L X /"-/'_ X 



88 30 96 30* 



Where 



/" represents the force of aqueous vapour at tempera- 

 ture of dew-point. 



/' represents the force of vapour at temperature of eva- 

 poration. 



d represents the difference between dry and wet ther- 

 mometers. 



h height of Barometer. 



