The Weather 3 



such as extreme cold or heat, and violent storms, cannot be 

 controlled or modified by human power, the discomfort and in- 

 convenience which they cause may be avoided in large measure. 

 To avoid them, however, it is necessary to know beforehand 

 what sort of weather is likely to come. This men have learned 

 to do by discovering and interpreting the conditions which 

 are supposed to control the succession of weather changes. 

 Those who have made a thorough study of such conditions 

 and their significance are able to predict with a high degree 

 of accuracy weather changes for one, two, or even three days 

 in advance. 



Any prediction of daily weather changes depends for its 

 degree of probability upon the kind and extent of the observa- 

 tions. If the important conditions of the atmosphere are not 

 observed, or are observed inaccurately, the predictions of 

 weather changes will be untrustworthy. If, however, the con- 

 ditions are observed carefully and accurately, and then inter- 

 preted properly, the weather may be forecast with a fair degree 

 of probability. If such observations be made with the aid of 

 instruments such as the thermometer and barometer, the 

 prediction will have a higher degree of probability. When the 

 local observations are supplemented with reported observa- 

 tions of the whole continent, a prediction based thereon will 

 be almost certain of fulfillment. A forecast made in this 

 manner is invaluable to men, for it makes it possible for them 

 to prepare for unfavorable extremes of weather and thus to 

 experience a minimum of loss or discomfort and a maximum of 

 profit. 



The conditions of the atmosphere which must be observed in 

 order to make dependable forecasts of weather changes, are : 

 (1) the appearance of the sky, as at sunrise and sunset, or the 

 halo around the sun or the moon ; (2) the form and movement 

 of the clouds ; (3) the direction, force, and shifting of the 

 winds ; (4) the temperature ; (5) the relative humidity or 

 moisture of the atmosphere, which may be felt in its effect 



