138 



TABLE 119. 



REDUCTION OF BAROMETER TO STANDARD GRAVITY. 

 Free-air Altitude Term. Correction to be subtracted. 



The correction to reduce the barometer to sea-level is (gi g)/g X B where B is the barometer reading and g and 

 |i the value of gravity at sea-level and the place of observation respectively. The following values were computed for 

 free-air values of gravity gi (Table 565). It has been customary to assume for mountain stations that the value of 

 gi = say about J the free-air value, but a comparison of modern determinations of gi in this country shows that little 

 reliance can be placed on such an assumption. Where gi is known its value should be used in the above correction 

 term. (See Tables 566 and 567. Similarly for the latitude term, see succeeding tables, the true value of g should be 

 used if known; the succeeding tables are based on the theoretical values, Table 565.) 



SMITHSONIAN TABLES. 



