4 Introduction to the Study of Science 



upon the skin or the mucous membrane of the nose and throat ; 

 (6) the pressure of the air, sometimes vaguely described as the 

 " lightness " or " heaviness " of the air. 



II. A STUDY OF WEATHER MAPS 



5. A typical forecast. The weather forecast for Saturday, 

 December 25, 1915, as published in the morning papers of New 

 York and vicinity was as follows : " For eastern New York, 

 rain in the south and rain or snow in northern portions to-night. 

 Sunday clearing and colder; strong southerly winds, shifting 

 to westerly." The changes occurred as predicted. Who made 

 the prediction? How was it known what weather changes 

 would occur in this particular region? 



Weather forecasts are made by expert officials of the Weather 

 Bureau of the Department of Agriculture of the United States. 

 Any person with practice and knowledge of the few principles 

 involved may make fairly probable forecasts for one or perhaps 

 two days. 



6. How weather maps are made. At government weather 

 stations, which are distributed at advantageous points through- 

 out our country, daily observations are made at eight o'clock 

 morning and evening (Washington time). Observations are 

 made of the temperature and pressure of the atmosphere, the 

 state of the weather, whether cloudy or clear, the direction and 

 force of the wind, and the precipitation of rain or snow for the 

 past twelve or twenty-four hours. This information is re- 

 ported by telegraph immediately to Washington, Boston, 

 Chicago, San Francisco, New Orleans, and other centrally 

 located cities, where it is recorded upon large outline and 

 topographical maps of the United States. Forecasts are then 

 made of changes to be expected within the following twenty- 

 four to thirty-six hours. The map is printed and copies are 

 mailed for distribution less than half an hour after receiving 

 the reports. The predictions are communicated to the Press 

 and to stations where weather signals are displayed. In case 



