876 



Handbook of Nature-Study 



the whole of the inhabited part of the western hemisphere north of the 

 equator. Any sort of disturbance within this vast region is photographed 

 at once upon the weather map. If it be a West Indies hurricane or other 

 destractive storm, its character is recognized instantly, its rate and direc- 

 tion determined and information of the probable time of its arrival sent to 

 those places that lie in its path. The method is perfectly simple. Anyone 

 with a weather map and a little experience can forecast the weather with 

 some degree of accuracy, or, at least, gain an intelligent understanding of 

 the conditions upon which the forecasts that accompany the map are based. 



Maps, Where Published and How Obtained 

 Weather maps are published in many daily papers, and in somewhat 

 larger form and more in detail, at many Weather Bureau stations. They 

 may usually be obtained for school use by applying to the nearest Weather 

 Bureau station or to the Chief of the Weather Bureau at Washington, D. C. 

 The forecasts that accompany the maps are simply an expression on the 

 part of the official forecaster as to the weather changes he expects to occur 

 in various parts of the country within the time specified, usually within 36 

 to 48 hours. His opinion is based upon the conditions shown by the map. 

 He has no secret source of information. You may accept his conclusions, 

 or, if in your opinion they are not justified, you have all the information 

 necessary to make a forecast for yourself. Weather maps are published so 

 extensively with a view to thus stimulating an intelligent interest in the 

 problem of weather forecasting, and also that one may see at a glance 

 what the temperature, rainfall, wind and weather is in any part of the 

 country in which he may be interested. The friends of the weather service 

 are those who best understand its work. 



The Value op the Weather Service 

 No one knows so well as the forecaster that the 

 changes that appear most certain to come some- 

 times fail, or come too late; but taking all in all, 

 about 85 out of 100 forecasts are correct. Of 

 those that fail, probably not more than three of 

 four per cent, fail because the changes come 

 unannounced. Most forecasters predict too 

 much, and their forecasts fail because the expected 

 changes come after the time specified or not at all. 

 It is fortunate that this is so ; for it is better to be 

 prepared for the change though it be late in co miug 

 than to have it come without warning. 

 The value of the weather service to the agriculture and commerce of the 

 United States cannot be questioned seriously. That the appropriations 

 for its support have been increased year by year from $1,500 in 187 1 to 

 nearly $1,500,000 in 1910 is evidence of its value and efficiency. A con- 

 servative estimate places the value of property saved by the warnings issued 

 by the Weather Bureau at $30,000,000 annually. 



Snow crystal. 



Photomicrograph by 

 W. A. Bentley. 



