56 ELEMENTS OF GENERAL SCIENCE 



While it is not possible to foretell the weather with cer 

 tainty, the predictions that are made are fairly accurate and 

 have been of great value. 



All forecasting of weather is based upon the weather map. 

 The map is made up each day from the reports telegraphed 

 from the observation stations all over the country. The pre- 

 dictions are based almost wholly on knowledge of the char- 

 acter and actions of cyclones. The usual path of cyclones 

 and the rate of motion have been carefully studied, and it 

 is possible to estimate quite closely what a cyclone will do 

 within the next twenty-four hours, and therefore how weather 

 conditions will change. For instance, if it were found that 

 within twenty-four hours a cyclone that is now in the West 

 could %e expected to approach to within a short distance of 

 a certain place, it would be safe to predict clouds and rain 

 for that place. On the other hand, the approach of a high- 

 pressure area would justify the prediction of clear weather. 



The difficulties in forecasting are many, and most of them 

 arise from the irregularities in the behavior of cyclones. If 

 all cyclones moved in the same path at the same rate and 

 did not change in violence, we should be able to predict the 

 weather with almost absolute certainty. But cyclones some- 

 times travel in unexpected directions or at unusual rates. 

 Sometimes they disappear entirely, and sometimes new ones 

 make their appearance without any warning. In spite of all 

 these difficulties the art of forecasting the weather lias been 

 brought to a high degree of reliability. 



The storm warnings at ports on the ocean and Great Lakes 

 are the means of saving annually many lives and hundreds 

 of thousands of dollars' worth of property. The warnings of 

 frosts have saved in a single year as much as $3,000,000 

 worth of perishable property in the form of fruits and 

 vegetables. Flood warnings are another important part of 

 the work of the bureau, 



