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 (.?i — ^)/? X B where B is the barometer reading and g and 

 gi the value of gravity at sea-level and the place of ol)servation respectively. The following values were computed for 

 free-air values of gravity «i (i'able 563J. It has been customary to assume for mountain stations that the value r>f 

 gi = say about 5 the free-air value, but a comparison of modern determinations of i'l 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. (Sec 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. 



