How to Foretell Fvostn. o45 



deposited, and when this is about or below 32*^ F., i.e., freezinor-point, 

 a frost may be expected unless winds arise or clouds form to 

 prevent it. 



The readings of the dry and wet-bulb thermometers are taken 

 during the afternoon, most particularly, however, about sunset. By 

 taking a series of earlier readings we can ascertain whether the 

 tendency to freeze is increasing or not. 



To explain the method of working, let us suppose the dry-bulb 

 tempeiature is -iOo R, and that of the wet-bulb, 35*^ F., consequently 

 the dit?erence between the readings is 5°. 



We take the vertical column 40'\ and the horizontal line o^. By 

 following the figures opposite and below these respectively, we find 

 the figures 6 5'^^* given as the amount to be subtracted from the wet- 

 bulb reading to obtain the dew-point. From the So^ record we 

 deduct i]')^, and get 28o*\ which is the dew-point required. As this 

 is below freezing point (320 y.), a frost may be anticipated, unless, as 

 already explained, clouds form or winds arise to prevent it. 



