36 



CONSTRUCTION OP ISOBARIC CHARTS 



must be performed in order to raise one pound from sealevel to the level of the station 

 barometer in Omaha. From now on the numbers of these level surfaces of gravity 

 will be expressed in even tens, since the heights are not measured closer than to 

 one foot. 



If now we substitute in (1) the value of gravity obtained from (2) and continue 

 the integration from the surface of the earth up to the elevation z above sealevel, we 

 obtain the ordinal number V of the level surface that passes through the point at the 

 elevation z. We find 



T'= t; + 0.464 8765r„(3 - 2„)(1 - 0.000 000 047 85(3 - zj) 



where z — Zq is the elevation of the point above the earth's surface. If this elevation, 

 z — Zqj be represented by z^ then we have 



F= T; + 0.4(54 876^(,s,(l - 0.000 000 047 852,). 



(•5) 



The calculation of V is much simplified by using the small Table I, which con- 

 tains the value of the quantity 0.464 876 X 2,(1 - 0.000 000 047 85zi) for each 1 000 

 feet of elevation above the earth's surface. 



Table 1. 

 0.464 876 X2i(l — 0.000 000 047 SSzj). 



Thus to calculate V for Omaha, we must, according to formula (5) multiply the values 

 given in Table 1 by ^o = 32.160 and then add tlie quantities thus obtained to 

 To = 18 550. We thus obtain the values given in Table 2. 



