BAROMETRICAL TABLES. XXV 



TABLES 14, 16, 16. 



Tables 14, 15, 16. Reduction of the barometer to sea level — English 



measures. 



Table 14 gives values of 2000 x m. 



Z I 



m 



56573 + 123. 1 ^-1-0.003 Z 1+^ 



The temperature varies by intervals of 2° from —20' F. to 96° /^, 

 except near the extremities of the table where the interval is 4° The alti- 

 tude Z varies by intervals of 100 feet from 100 to 9000 feet. The values 

 of 2000 m are given to one decimal. 



In order to facilitate interpolations for iractions of a 100 feet in 

 altitude, the tabular differences for 100 feet have been added on each line. 



Table 15 gives a small correction to 2000 m for latitude, computed 

 from the expression 



2000 wz X 0.002662 cos 2^. 



The arguments are 2000 w, which varies by tens from 10 to 350, and 

 the latitude, which varies by 5° from 0° to 90? The correction is to be 

 subtracted for latitudes below 45° and added for latitudes above 45! The 

 tabular values are given to one decimal. 



Table 16, with the value of 2000 ?» thus corrected, gives the correction 

 which must be applied to the barometric reading B (corrected for tem- 

 perature) to reduce it to sea level. The arguments are B, which varies by 

 0.5 inch from 31.00 inches to 19.5 inches, and values of 2000m, which are 

 given for every unit from i to 334. 



The reduction values B^ — B are given to o.oi inch. 



Example : 



]>t ^=26.24 inches be the barometric reading (corrected for temper- 

 ature) observed at a station whose altitude is 3572 feet, and latitude 

 32? Suppose the mean temperature of the air column Q = 63^0 F. 



Table 14 gives (p. 63) with Z= 3,500 feet and ^ = 62r8 F., 20oow = 108.0 

 The difference for 72 feet is 2.2 



The approximate value of 2000 m is no. 2 



Table 15, with 2000 m = no and latitude = 32°, gives the subtractive 

 correction o. i. Hence the corrected value of 2000 w is no. i. 



With 200ow = iio.i and ^ = 26.24, Table 16 (p. 72) gives the reduc- 

 tion to sea level, 3.55 inches. Accordingly the barometric pressure reduced 

 to sea level is 



B, = 26.24 + 3.55 = 29.79 inches. 



