USE OF THE BAROMETER 87 



very closely connected with changes in the weather. The 

 barometer does not directly foretell the weather, but a low or 

 falling pressure, accompanied by a simultaneous fall of the 

 mercury, usually precedes foul weather, while a rising pres- 

 sure, accompanied by a simultaneous rise in the mercury, 

 usually precedes fair weather. The barometer is not an in- 



FlG. 48. Barograph. 



fallible prophet, but it is of great assistance in predicting the 

 general trend of the weather. There are certain changes in 

 the barometer which follow no known laws, and which allow 

 of no safe predictions, but on the other hand, general future 

 conditions can be fairly accurately determined. Figure 48 

 shows a barograph or self-registering barometer which auto- 

 matically registers air pressure. 



Seaport towns in particular, but all cities, large or small, 

 and villages too, are on request notified by the United States 

 Weather Bureau ten hours or more in advance, of probable 

 weather conditions, and in this way precautions are taken 

 which annually save millions of dollars and hundreds of lives. 



