The Weather 



17 



FIG. 6. Barograph. Note differences be- 

 tween barograph and thermograph. Explain 

 how each works. 



The aneroid or not- 

 liquid barometer (Fig. 

 7) consists chiefly of a 

 cylindrical metal box 

 made of thin corru- 

 gated steel or German 

 silver, with an elastic 

 top, and a mechanism 

 to show upon the dial 

 the differences in air 

 pressure. The box is 

 a partial vacuum, so that an increase of pressure upon the 

 top forces it inward, and a decrease allows it to curve out- 

 ward. The pointer attached indirectly to the box indicates 

 the air pressure on the dial in " inches 

 and fractions thereof " in correspond- 

 ence with the readings of the mercury 

 barometer. The legend usually found 

 on the dial of the aneroid barometer, as 

 " Stormy," "Rain," " Fair," "Change," 

 " Very Dry," is of little or no value. 

 The aneroid is made to meet many 

 different needs, such as those of trav- 

 elers and engineers as well as for sta- 

 tionary use. It is sometimes made to 

 FIG 7 Aneroid g * ve ^ e altitudes f or the readings of 

 barometer. air pressure. 



SUMMARY 



Men cannot control weather changes. They can predict changes 

 and make provisions to meet them. 



Weather predictions are made more reliable by use of such instru- 

 ments as the barometer, thermometer, and hygrometer, and by tak- 

 ing into account conditions over wide areas. 



Weather conditions observed for forecasting are (1) the appear- 

 c 



