56 CONSTRUCTION OF ISOBARIC CHARTS 



Between p = 24.5 and p = 24.0, t^ = 69.5 

 " p = 24.0 " p = 23.5, t^ = 67.5 

 " p = 23.5 " p = 23.0, t^ = 65.0 

 " ^ = 23.0 " p = 22.5, <^ = 62.5 



For these values of tr Table 9 gives the following : 



Finally, to calculate the quantities F31.0, ^30.5, F30.0, F29.5, etc., we must first deter- 

 mine the number Fp_ of level surfaces of gravity lying between sealevel and the first 

 of the isobaric surfaces just named which the balloon meets as it rises into the air. 

 This number consists of two parts, viz., Vo = the number of level surfaces lying between 

 sealevel and the station-barometer, and EjJ^ = the number of level surfaces lying 

 between the station-barometer for which the pressure is jh, and the isobaric surface 

 p — jjj. Vo is a constant and has already been computed for Omaha so that it only 

 remains to obtain the quantity EJ5^ To accomplish this we use formula (23), written 

 in the following form : 



Ep, = 1837.3 X 509.4 x log^° + 1837.3(<, - 50° F.) log^\ 



Pi Pi 



By writing 



this equation may be written 



1837.3 X 509.4 X log5' = (E?05o 



E^i = (E5;i).„ + ^^50974- (E?o«. 



Table 12 contains the values of (E^;)5o considered as a function ofjh and po. 

 Table 13 contains the values of the expression "l „ „ . (E^;)5o considered as a func- 

 tion of (EP;)go and /,,.. Of course the difference p^ — pii never exceeds 0.5 inch. 



In the illustrative example for Omaha, p^ = 28.496, p)i — 28.0, and tr = 68.0, 



whence from Table 12 {W;^^^ = 7 130, and from Table 13, ^^^- m>%o = + 250. 



Thus the number of level surfaces lying between the station-barometer and the 28.0- 

 inch isobaric surface equals 7 130 -f- 250 — 7 380. The number Vo of level surfaces 

 lying between sealevel and the isobaric surface of the station-barometer is 18 550. 

 The total number of level surfaces of gravity included between sealevel and the 

 isobaric surface of 28.0 inches, is therefore F28.0 = 25 930. 



