190 



THE WEATHER 



the mountain. This Perier did on September 19, 1648, and 

 Pascal's theory was confirmed (Fig. 134). 



The barometer is used in studying the weather. The 

 weather stations of the United States are at many different 

 elevations. Barometer readings at sea level are ordinarily 

 about 30 in.; at the altitude of Chicago, about 29.4 in.; at 

 Denver, about 23 in.; and at the top of Pike's Peak, about 15 

 in. Scarcely any two weather stations have the same ele- 

 vation. Therefore, in order to compare barometer readings 

 with those of other weather observers, all readings must be 



^V/f^rfc^.*-^^^ 



^K^-.V ^-+ : +~^:^j?*$ 



6 



FEET? 



4ZZ40- 



o-SEA LEVEbo- 

 Fio. 134. Atmospheric pressure varies with altitude. 



PRESSURE 

 IMINCHES 



or 



MERGUKY 



7.9 

 -10.2, 



corrected for altitude as well as for temperature. In doing 

 this it is customary to change all readings to what they would 

 have been if the barometer had been at sea level. These 

 corrections are easily obtained from Table X. 



DIRECTIONS FOR USING TABLE X. The proper correction is found 

 from Table X in a manner similar to that followed in using Table IX. 

 This correction, however, is added to the barometer reading. 



NOTE. Extensive tables for the correction of barometers for any alti- 

 tude from the sea level up to several thousand feet have been prepared. 

 It is intended that the teacher or student wishing to use this book at an 

 altitude not given in this table shall ascertain the corrections necessary 

 at the required altitude and the various temperatures by applying to some 

 nearby weather station, and record them on the line marked X, 



