2 THE WEATHER 



aneroid barometer (about the size of a watcli) costs about $12. 

 These instruments are arranged to determine elevations as well as to 

 give weather indications. 



Mercurial barometers are more expensive, costing S25 to S40. As 

 the mercury in the column of a mercurial barometer changes its 

 length with changes of temperature just as the column of mercury 

 does in a mercurial thermometer, it is necessary to correct the read- 

 ing at each observation. Tables, giving the amount to be added or 

 subtracted from the reading for each degree of temperature, should 

 be secured when the instrument is purchased. 



Thermometers should be exposed in the shade, and where there is 

 a free circulation of air. Barometers should not be exposed to full 

 sunshine for any great length of time. Any convenient place in the 

 house will give proper exposure for barometers. 



How to use the Weather Map 

 (Weather Bureau, U. S. Dept. Agric.) 



The first impression of a student of the weather maps, as they pre- 

 sent their seemingly endless forms and combinations of the temperature 

 and pressure lines, is often one of confusion. This feeling is likely 

 to be attended by one of discouragement, and the impulse to abandon 

 the task of seeking an underlying plan is more powerful with many 

 persons than the incentive, which depends upon curiosity, to know 

 what it all really means. 



The storm-tracks. 



The storms of the United States follow, hoTvever, year after year a 

 series of tracks, not capricious, but related to each other by very well- 

 defined laws. 



The i^ositions of these tracks have been determined carefully for 

 the United States by studies made in the Forecast Division of the 

 Weather Bureau, on the long series of maps that have been made during 

 the past twenty years. The track that the central point of a high area 

 or that the center of a storm follows in passing over the country from 

 west to east is laid down on individual charts, these are collected on 

 a group chart, and from this the average track i)ursued can be readily 

 described. The chart herewith (see fig. 1) shows the general result of 



