608 



TABLE 645.— REDUCTION OF BAROMETER TO STANDARD GRAVITY FOR 



DIFFERENT HEIGHTS 



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 gi the value of gravity at sea level and the place of observa- 

 tion respectively. The following values were computed for free-air values of gravity gi 

 (Table 802). 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 g\ in this 

 country shows that little reliance can be placed on such an assumption. Where <7i is known 

 its value should be used in the above correction term. (See Tables 803-805.) 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 802.) 



Height 



above 



sea level 



meters 



100 



200 



300 



400 



500 



600 



700 



800 



900 

 1000 

 1100 

 1200 

 1300 

 1400 

 1500 

 1600 

 1700 

 1800 

 1900 

 2000 

 2100 

 2200 

 2300 

 2400 

 2500 

 2600 

 2700 

 2800 

 2900 

 3000 

 3100 

 3200 

 3300 

 3400 

 3500 

 3600 

 3700 

 3800 

 3900 

 4000 



Observed height of barometer in mmHg 



9\ ~ 9 



400 



450 500 



550 



600 



650 



700 



750 



800 



.031 Correction in mmHg to be sub- .02 .02 .02 — 



.062 tracted for height above sea level .04 .05 .05 — 



.093 in first column and barometer read- .07 .07 .07 — 



.123 ing in the top line. .09 .10 .10 — 



.154 ______ .11 .12 .13 - 



.185 _____ .12 .13 .14 — — 



.216 _____ .14 .15 .16 — - 



.247 _____ .16 .18 .19 — — 



.278 _____ .18 .20 .22 — — 



.309 — — — .18 .19 .20 .22 .24 — — 



.339 — — — .19 .21 .22 .24 — — — 



.370 — — — .21 .23 .24 .26 — — — 



.401 — — — .22 .24 .26 .29 — — — 



.432 — — — .24 .26 .28 .31 — — — 



.463 — — .24 .26 .28 .30 .33 — — — 



.494 — — .25 .28 .30 .32 — — — — 



.525 — — .27 .30 .32 .34 — — — — 



.555 — — .28 .31 .34 .36 — — .020 .0463 



.586 — — .30 .33 .36 .39 — — .019 .0447 



.617 — .28 .31 .34 .38 .41 — .021 .019 .0432 



.648 — .30 .33 .36 .40 — — .021 .018 .0416 



.679 - .31 .35 .38 .41 — — .020 .017 .0401 



.710 — .32 .36 .40 .43 — .021 .019 .017 .0386 



.740 — .34 .38 .42 .45 — .021 .018 .016 .0370 



.771 .31 .35 .39 .43 .47 — .020 .018 .015 .0355 



802 .33 .37 .41 — — .021 .019 .017 .015 .0339 



.833 .34 .38 .42 — — .020 .018 .016 .014 .0324 



.864 .35 .40 .44 — — .019 .017 .015 .013 .0308 



.895 .36 .41 .46 — .020 .018 .016 .015 .013 .0293 



.926 .38 .42 .47 — .019 .017 .016 .014 .012 .0278 



.957 .39 .44 — — .018 .016 .015 .013 — .0262 



.988 .40 .46 — — .017 .015 .014 .012 — .0247 



1.019 .42 .47 — .017 .016 .014 .013 — — .0231 



1.049 .43 .48 — .016 .015 .013 .012 — — .0216 



1.080 .44 .49 — .015 .014 .012 .011 — — .0200 



1.111 .45 — — .014 .013 .011 — — — .0185 



1.142 .46 — — .013 .012 .011 — — — .0170 



1.173 .48 — .012 .011 .011 .010 — — — .0154 



1.204 .49 — .011 .010 .010 — — — — .0139 



1.235 .50 — .010 .009 .009 — — — — .0123 



— .008 .008 .007 .007 Corrections in in. to .0092 



.006 .005 .005 .004 — be subtracted for height .0062 



.003 .003 .003 — — above sea level in last .0031 



column and barometer 



reading in bottom line. 



30 28 26 24 22 20 18 16 14 g x - g 



Observed height ot barometer in inches 



15000 



14500 



14000 



13500 



13000 



12500 



12000 



11500 



11000 



10500 



10000 



9500 



9000 



8500 



8000 



7500 



7000 



6500 



6000 



5500 



5000 



4500 



4000 



3000 

 2000 

 1000 



feet 

 Height 



above 

 sea level 



SMITHSONIAN PHYSICAL TABLES 



