66 



CONSTRUCTION OP ISOBARIC CHARTS 



Here the quantities ^ig 550, ^20000) etc., are the barometric pressures at the level sur- 

 faces r= 18 550, V = 20 000, etc. From the {t„ F)-curve for 8 A. M. in Fig. 2, we 

 find corresponding values of tr for the same level surfaces as follows : 



For F, 

 for F.,„ 

 for 

 for 

 for 



for 

 for 

 for 

 for 

 for 

 for 

 for 



„,^ p = 28.496, <, = 67.0 

 .0 000 i> = 28.398,^=67.5 

 F3„„„„i> = 27.732,^^=71.0 

 T^oooo P = 27.087, ^^=74.0 

 F,„ „„„p = 26.458, <,= 74.0 

 F,, „„„;; = 25.844,^^=72.5 

 T%„ 000? = 25.241, <^= 71.0 

 ^«o 000 i^ = 24.651,/^ =70.0 

 T^^ 000? = 24.074,^^=69.0 

 ^",00 000^= 23.509,^^=66.0 

 F,o 000 P = 22.954,^ = 63.5 



^120 000 P = 22.409,/^ = 61.0 



By plotting the above values of p and tr as a system of coordinates in which p is 

 ordinate and the corresponding value of t^ is abscissa, a curve is obtained which shows 



Fig. 3. The (/>, (r)-curve of virtual tem- 

 peratures at Omaha for each vahie of atmospheric 

 pressure as calculated for 8 a. m., 70th meridian 

 time, from the kite record of September 23, 1898. 



